Can a rifle really be this sensitive to ammo?

[Merle1]

I think a lot depends on the rifle. I've owned some that would shoot very well with specific loads, poorly with others. All of them will do better with some ammo, but I've owned several rifles that would do pretty darn good with most anything you put in them.

This sums it up neatly. Each rifle is a law unto itself!

 

[bikemutt]

MtnCreek said:

If you still have some of the poor performing ammo, might be interesting to test agaibut reverse the order they are fired.

Good point, the rifle may just shoot poorly with a cold barrel, or maybe the shooter shoots poorly to start with. If I had not seen this rifle shoot horrible with 168 gr Hyper Clean before I'd be looking for other things. And, that ammo does fine in my bolt guns, not great, but not 8 moa.

The rifle has been an enigma, but, when it gets what it likes, it shoots good.

Someone mentioned trigger; it came with a Giesele SSA 2-stage which is not too bad. I have an SSA-E laying around which I'll install soon.

 

[jbloader]

I have a Chinese Mosin carbine that I can consistently bust clay pigeons with at 100yrds on irons and Russian milsurp. I paid less than $100 for it, it's dated stamped 1953, it's Russian manufactured, Chinese abused, and not quite the "poor shooting rifle" that some would like to make them out to be. In fact, I would say that it is shooting a damn sight better than the new American rifle the OP is having issues with. Verify the bore and bolt before you buy, but it is one of the most enjoyable rifles to shoot that I own. And, yes, it kicks.

To the OP's issue. I took some Perfekta (new rifle caliber and all that was available was the WalMart stuff) ammo out to allow my daughter to shoot her new Remington .223 and "flyer" was the word of the day. A week later we came back with a Fiocchi load that others had success with and my daughter was shooting @ MOA at 100m. I would check the ammo first, fwiw.

 

[Tirod]

There is a big difference in the way a self loader jams the cartridge into the chamber, and a bolt action. That is the reason most military cartridges use crimps - to keep the bullet from setting back. Variations in bullet seating depth cause variations in groups as the leade is significantly different one round to the next.

When the bullet is pushed forward into the chamber it strikes the ogive and can be pushed back further in the neck. On ignition the round has to move forward more, or less, for each shot before engaging the grooves. It can also tip the nose to some degree, and what you get is a bullet that is no longer coaxial with the barrel emerging from the muzzle with some degree of yaw. The more, the worse the accuracy. It's why precision target shooters also measure the coaxial loading of the bullet in the case, to get it in the same line as the center of the barrel. .004" in that regard is considered a huge amount of inaccuracy. .002" is run of the mill, under .001" tough to achieve but the goal.

If loose necks allow the bullet to be loaded crooked they will go down the bore crooked. Self loading actions need different loads than manually operated ones and the difference is crimped necks.

 

[FL-NC]

Yes. I have rifles that just don't like some types of ammo.

 

[joem1945]

I have several rifles that are ammo sensitive. One AR15 is only accurate with Nosler 69 gr bullets. Other 69 gr bullets open the group up quite a bit.

 

[Bart B.]

Tirod's remarks:

There is a big difference in the way a self loader jams the cartridge into the chamber, and a bolt action.

In my observations of high speed videos of both operating, there’s no difference with box magazines (fixed or detachable) except for speed. Some match rifle competitors shooting rapid fire matches (10 rounds in 50 seconds reloading with a 5-shot stripper clip half way through the string) manually cycle the bolt not much slower than Garands do.

That is the reason most military cartridges use crimps - to keep the bullet from setting back.

The major force pushes the cartridge forward which will propel the bullet forward if it’s not gripped tight enough.

According to arsenal people I’ve talked with, bullets in arsenal ammo used in combat are crimped in to prevent them from shifting (typically back into the case) due to shipping and handling before they’re chambered in the barrel. Specifically those used in belts used in full auto weapons or are subject to all sorts of field conditions before loading and chambering. M72 30 caliber match ammo had the cannelure removed from the 172-gr. FMJBT machine gun bullet and case mouths were no longer crimped into them when the arsenals learned they shot more accurate without all that bad stuff got stopped. Military teams oft times pulled those bullets then replaced them with commercial match bullets and those shot even more accurate. Even in semiauto use, the lesser grip on those bullets still held them tight enough and no bullets slipped forward upon chambering in M1 nor M14 rifles.

Variations in bullet seating depth cause variations in groups as the leade is significantly different one round to the next.

That's the variation in bullet jump distance. The leade (or throat, as it’s sometimes called) is that part of the chamber where the rifling starts a few thousandths larger than bullet diameter then tapers down to bore diameter. It stays the same from shot to shot except for erosion from burning powder that lengthens it a thousandth inch for every few dozen shots fired. And most important, unless you shoot your stuff no worse than 1/3 inch at 100 yards, you probably won’t see any difference in bullet seating depth over near 1/10th inch with good ammo properly tested.

When the bullet is pushed forward into the chamber it strikes the ogive and can be pushed back further in the neck.

Only if the round’s bullets are seated out too far or not gripped tight by the case neck. Military ammo’s bullets are such that there’s several thousandths space between the bullet and origin of the rifling. Reloaders get to choose whether or not the bullet touches the lands and sets back when chambered.

On ignition the round has to move forward more, or less, for each shot before engaging the grooves.

Virtually all military ammo is fired in weapons with a plunger type ejector in the bolt face. When the round’s are chambered and the bolt locks into battery, that ejector pushes the case forward until its shoulder stops against the chamber shoulder. Case head clearance to bolt face is less than case head clearance to extractor lip; has to be that way to ensure reliable extractor lip easily slipping over the chambered case rim. When the firing pin strikes the primer, the round fires in place and doesn’t move at all; except for a few thousandths setback of the shoulder on bottleneck cases caused by firing pin impact. Col. Hatcher’s tests showed .30-06 ammo shoulders setting back as much as .007".

It can also tip the nose to some degree, and what you get is a bullet that is no longer coaxial with the barrel emerging from the muzzle with some degree of yaw. The more, the worse the accuracy. It's why precision target shooters also measure the coaxial loading of the bullet in the case, to get it in the same line as the center of the barrel. .004" in that regard is considered a huge amount of inaccuracy. .002" is run of the mill, under .001" tough to achieve but the goal.

With a perfectly straight round chambered, it will always be crooked a tiny amount. Bottleneck cases headspacing on their shoulder have their shoulder hard into and well centered in the chamber shoulder. The back end of the case just forward of the extractor groove is pushed off center by the extractor pushing it against the chamber wall. No part of the new case body touches the chamber wall forward from that point all the way to the shoulder because the case diameter at the shoulder is smaller than that place in the chamber. For every .001" the back end of a .308 Win case is off center in the chamber, the bullet tip will be about .0005" off center in the bore. The bullet tip is about half the distance from mid point on the case shoulder as the case body at the extractor groove is from that same shoulder point.

If loose necks allow the bullet to be loaded crooked they will go down the bore crooked.

Bullets seated with minimal grip by the case neck they can easily be pulled out by hand shoot very accurate. .308 Win ammo’s been loaded with .003" bullet runout that’s shot inside 3 inches at 600 yards for a couple dozen shots properly tested. Military teams testing match grade M1 and M14 service rifles with arsenal match ammo see no improvement in accuracy with ammo having less than .003" runout. The old standard of runout not exceding 1% of bullet diameter seems to be good. But there’s several thousandths spread in bullet runout for a given round depending on which runout tool’s used. None of them made to date I know of hold the cartridge like its chambered in the barrel so whatever’s shown on the runout tool won’t match what it is in the barrel.

Self loading actions need different loads than manually operated ones and the difference is crimped necks.

Myth 43 on the list of many.

 

[kimberauto]

Heres my .260REM reloads
First picis when it was cold bore and clean and the second pic is when it started to warm up after 5shots.

 

[kimberauto]

 

[kimberauto]

Can't figure out how to post pics

 

[Gtscotty]

And most important, unless you shoot your stuff no worse than 1/3 inch at 100 yards, you probably won’t see any difference in bullet seating depth over near 1/10th inch with good ammo properly tested.

I've seen you make this statement in other threads, and I'm curious how you came to this conclusion? Was it your own testing, or is there some test data on the subject that you could direct me to? I ask because I've almost always found seating depth to affect groups when working up new loads. While some bullets seem less sensitive to seating depth (Sierras), I've found the performance of others (Hornady SST's and Nosler Accubonds), to be quite affected by seating depth. If there is some published testing on the effects seating depth that says I'm wasting money and time, I'd love to know about it.

 

[JohnKSa]

I have one Swedish Mauser that will make pie-plate sized groups with Remington ammo but will put the Swedish surplus into about an inch @ 100 yards.

 

[kimberauto]

Well right now my test loads were seated to factory specs which is 2.780 that's between 15&20 thousandths off the lands.
My next load is gonna be 5 thousandths off will let you know .

 

[Bart B.]

Gtscotty, I came to those conclusions after two different things.

First was when taking a tour of Sierra Bullets plant in California back in the 1960's. Their head ballistician showed me how they reloaded .308 Win cases testing most of their 30 caliber bullets for accuracy. He was also a friend I shot rifle matches with as well as being a top ranked competitor in his own right. He had tried different seating depths on their bullets and in standard SAAMI spec chambers (what they used in their test barrels), he saw insignificant difference in 10-shot test groups' sizes across near 1/10th inch spread in seating depth. Their best lots of match bullets had about 1/10th inch better accuracy in a narrow range of about .030" or so. That's hard to discriminate when their average groups were around 1/4 inch in their 100 yard range with match bullets in match barrels.

Their reloading manual's loads tested in commercial rifles were not as accurate and a 1/10th spread in seating depth was virtually the same for accuracy in them.

Second was my own tests shooting 200 and 300 yard matches with a 1/10th spread in seating depth also showed no significant difference in accuracy. 10-shot test groups were near 1/2 MOA at 200 and 2/3 MOA at 300 yards. Considering the fact that the most accurate benchrest rifles and ammo shot 4/10ths and 5/10ths respectfully at those ranges, I thought that was about as good as I could get.

At ranges 600 yards and greater, there was a small difference but only about 1/4 MOA. But I typically got best accuracy with Sierra, Norma, Lapua and Winchester bullets seated into the lands for long range use.

The icing on my decision making seating-depth cake was watching military and civilian teams use the same lot of ammo across lots of rifles getting great and equal accuracy across all of them. Even with different bore, groove and chamber dimensions. Then being one of those team members shooting ammo I'd never shot before.

There are bigger obstacles to overcome than seating depth. But with most people not shooting enough shots per test group to be meaningful, all sorts of accuracy claims will be had for a given load assembled some specific way then shot in a given rifle. I've used the same load and seating depths across many barrels and never saw any difference in accuracy.

All the above aside, what about the well know fact that good commercial match ammo (Federal, Black Hills, Hornady) shoots very accurate in most rifles? It's fixed seating depths must carry some weight in my opinion, shouldn't it?

 

[agtman]

When I check a gun / load combination for accuracy, I put sandbags under the gun for support, and on top of the barrel to help stabilize the gun. * * *

Well, if things like accuracy or obtaining a repeatable zero matter (e.g., for hunting, where you won't be shooting off a bench), that's exactly how you SHOULD NOT do it.

 

[Gtscotty]

Bart,

I appreciate your extensive experience in long range target shooting, but a quick search shows that:

Sierra
http://www.sierrabullets.com/resources/x-ring-newsletter/index.cfm/xid/4/What-Is-The-Palma-Bullet/

Nosler
http://www.nosler.com/blog/news-and-articles/2013/6/4/beyond-the-basics-developing-your-own-loads

Barnes
http://www.barnesbullets.com/load-data/

and

Berger
http://www.bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/

http://www.bergerbullets.com/wp-content/uploads/2013/03/COAL.pdf

All address seating depth or distance off lands to some extent on their websites. Why would this be the case if it was inconsequential to the accuracy of rifle loads?

All the above aside, what about the well know fact that good commercial match ammo (Federal, Black Hills, Hornady) shoots very accurate in most rifles? It's fixed seating depths must carry some weight in my opinion, shouldn't it?

It's true that .308 FGMM shoots well in a wide variety of rifles, but it is not always the best load for any given rifle. For example, FGMM will deliver 0.7 - 0.8 in 5 shot groups in my CTR, but my own tailored loads can consistently stay in the 0.5 in range, and sometimes a little less. I have read that Sierra bullets with their tangent ogive are quite a bit less sensitive to seating depth than other bullet designs with secant or hybrid ogives like Bergers and some Hornadys. This mirrors my experience, and I wonder if part of the reason that FGMM (and other match ammo brands using similar bullet designs) shoot well in many rifles is that accuracy provided by that bullet design is less subject to differences in distance to lands.

I should state that most of the loads I have developed have used hunting type bullets in light-ish hunting style rifles. I have noted that dedicated target bullets (such as the Nosler 168gr Custom Competition bullets) generally require less seating depth fiddling to get an excellent load than most dedicated hunting bullets. Perhaps minimizing seating depth sensitivity is an integral part of designing a target bullet that will provide the utmost accuracy in a wide variety of rifles.

 

[Bart B.]

Gtscotty, I checked those sites you listed for testing loads for the best seating depth. They all use only 1 or 2 few-shot groups to qualify a given seating depth. I don't think either's a good test. Especially when the most accurate rifles' seventy 5-shot groups across several days have a huge spread in size. And the first one for each day doesn't represent the average across several days.

In case you've never seen the results of several days of group shooting with any rifle, here's the track record of a top ranked benchrest competitor shooting the same rifle and ammo in seven different days of matches:



Remember all group's centers are not the same distance and direction from the aiming point. That further enlarges each day's 25-shot group composite of all five individual groups in each match.

How well does the first group at each range represent the average for that day or across all seven days? Or the second one, for that matter?

Therefore, I don't think those link's methods are very good for measuring the results of a given seating depth. But the average across 70 groups would be a good indicator.

If you read my earlier post stating that Sierra's tests showed only 1/10th inch change in groups across different seating depths, that was based on the average across dozens of 10-shot groups fired with a given load. Not one or two 3- to 6-shot groups those links suggest. I could not discern a 1/10th MOA change in accuracy in my accuracy tests at 200 and 300 yards shooting a few 20-shot groups with a 1/10th inch spread in bullet seating depth. If someone else can, so be it.

But it's popular across the shooting sports to conduct statistically insignificant tests to prove a point.

 

[Nature Boy]

That's informative and eye opening Bart. Thanks for sharing

 

[Bart B.]

Note those groups were shot with the rifle resting on bags and fired in free recoil. The shooter only touched the few-ounce trigger with a finger.

Had the rifle been held against his shoulder as it rested on those bags, the groups would have been larger. A much bigger spread from smallest to largest. This is how 99% of all rifle shooters test their stuff for whatever they want to measure. Their own variables in holding the rifle contribute to the groups being bigger. Sometimes 3 to 4 times bigger than what the rifle and its ammo is capable of when fired in free recoil.

Good news is, most rifles and ammo are more accurate than their owners shoot them.

 

[Gtscotty]

Bart,

I'm not sure how you came to the conclusion that I posted links to those websites as an example of how to test groups or seating depths. If you re-read my post all I stated was that a quick internet search turns up several examples of bullet manufactures (including Berger's very well regarded ballistician Brian Litz, and Sierra bullets) with publications on their sites stating that seating depth is one component of developing an accurate load.

Why would they say this if they had not seen an effect with their own bullets in multiple rifles? Do you think they have not shot large composite groups in the testing of their bullets? What point are they trying to prove with their statistically insignificant tests?

I did read your earlier post about Sierra bullets and their testing from the 60's, I was just hoping that you might be able to point me to some published testing that shows that seating depth is insignificant to accuracy. I've looked around and I can't find any testing or bullet manufacturer publications that indicate that bullet seating depth has marginal or no impact on accuracy... most of what I see indicates the opposite for many bullet designs.

On the topic of bullet designs, it seems a lot of your shooting was done with Sierra's which are known to generally be less seating depth sensitive than other designs. On the other end of the spectrum are Berger's, which, while one of the top target bullets available, are know to be sensitive to jump. At least that's what the company would have us believe... I'm having a hard time figuring out why Berger would go to the trouble of instructing their customers on finding the right seating depth if it didn't really matter? I guess I'm just not convinced that it's case closed on the importance of seating depth, especially with the dearth of actual data available, and the overwhelming number of shooters and companies that seem to think it matters.

To the OP, sorry for the thread hijacking.

 

[natman]

I decided to take my AR10 to the range today with a variety of ammo to see what it likes. Up until now I've run Norma match .308 through it with excellent results but, I've run out of that ammo so, time to try new stuff.

First up at 100 yards was 5 rounds of HPR 168 gr match. I just about lost it figuring everything from the scope must be loose to I'm drunk (I was sober). 8" or worse group from a Rainier Arms Select barrel?

Next up was Aquila 150 gr plinker ammo which I had very low expectations of; it's regularly 4 moa ammo for me, regardless of rifle.

Finally I fired 5 rounds of Hornady 168 match, low and behold that's what I expect from this rifle; sub-moa.

I guess I'm posting this because I've never seen a rifle so picky. I don't mind that as I'll feed it what it likes. Anyone here at THR noted this sort of ammo preference from a rifle?

Sounds to me like you've just found one load your rifle doesn't like, the HPR. The Aguila shot as well as it ever has and the Hornady shoots as well as you could possibly expect.

Moral of the story: Shoot the Hornady ammo.

 

[I6turbo]

Bart B.

Thank you for taking the time to post all of the detail you've posted here. And elsewhere, for that matter.