Good load in 20" not in 16" - how to fix


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CMV
January 1, 2012, 07:51 PM
So the rounds I worked up in a 20" HBAR 1:9 AR-15 were striking targets at the same POI at 50 yds and 100 yds as XM193. That's what I was going for - I don't want have to change sights or add clicks going back & forth between my loads & M193.

So today I decided to try them in the other rifle with a 16" M4 profile 1:9. I expected the velocity to be lower, but assumed I'd get the same POI results. My loads are striking a lot lower than M193 at 50 yds & 100 yds.

So that has me thinking I might be off altogether. If I were going out to 250 yds or 400 yds, would I be seeing the same thing out of the 20" barrel? I'm assuming same POI at 50 & 100 yds means I'm going to be fairly close through the entire effective range.

Anyway, it didn't occur to me to take both rifles while working up the load and measure both at every step along the way. I figured I'd go with the 20" to get closer to book fps and once it was good, it would "just work" in the 16" but with a velocity penalty for the shorter barrel.

Maybe what I want to do is impossible w/o exceeding max load by 6.25% and making carbon copy M193?

Or is there a way I can make rounds that will give me the same POI as M193 at various ranges in both rifles?

As of right now:

Load is 25.0gr H335, 55gr Hornady FMJBT, LC brass, CCI #41.

20":
M193 - 3270 fps
Mine - 3034 fps, 17.4 std dev, 50 yds = same POI, 100 yds = same POI

16":
M193 - 3022 fps
Mine - 2834 fps, 28.1 std dev, 50 yds = .9" low, 100 yds = 2.9" low

Since I shoot both rifles interchangeably, I want the same load to work in both. I don't want to have my ammo segregated into "stash", "load for 20", & "load for 16" lots. If this is possible while staying within published .223 data, what method for working up the load would be best?

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PigButtons
January 1, 2012, 08:08 PM
You may want to try a bit faster powder like Varget. This might get your velocities up closer to the M193. Just a thought because in my Lee manual there are 12 powders listed for that weight bullet that yield faster velocities than the H335. Most of them are faster burners than the H335 and in the shorter barrel this will have the biggest impact. Again, I'm no expert YMMV. Slower powders have better results velocity wise in longer barrels and visa versa

Fleet
January 1, 2012, 08:10 PM
Or is there a way I can make rounds that will give me the same POI as M193 at various ranges in both rifles?
Yes you can, but it's unlikely to be the same load that gets you there for both rifles.

helotaxi
January 1, 2012, 09:29 PM
The issue is that each barrel resonates differently and differently with each load. You have to mimic that resonance as well as the velocity of the "target load" to mimic the basic ballistics. Also, unless you are matching the ballistic coefficient of the XM193, you're POI matching will quickly diverge as the range increases.

Most of them are faster burners than the H335 and in the shorter barrel this will have the biggest impact. Again, I'm no expert YMMV. Slower powders have better results velocity wise in longer barrels and visa versa
This is false. A load with a high (relatively) velocity in a short barrel will also have a high velocity in a longer barrel. Slow or fast powder has no bearing on a load's suitability for a long or short barrel.

rcmodel
January 1, 2012, 09:40 PM
Or is there a way I can make rounds that will give me the same POI as M193 at various ranges in both rifles?Not unless you can sneak in and steal several pounds of the powder & bullets and primers and cases ATK is using at the Lake City Army Ammo plant to load M193.

Handloaders have no way of duplicating the exact burn rate of what is used in military ammo.

And as helotaxi said, every barrel is a law into itself when it comes to harmonics, etc with different loads.

The best you can do is come close to the velocity you want, then sight in each rifle for it and call it good enough for Goober-Mint work.

rc

CMV
January 1, 2012, 09:58 PM
Appreciate the replies.

I really don't care what the velocity is - I'm really just measuring it because other than where the rounds strike on paper I have no way of quantifying whether or not adjustments I make have a positive effect. I figure its also going to be an indicator of how consistent I am in my work - if I'm getting wild fps variations I would assume that some part of my process is out of control causing that.

I'm not trying to make an M193 replacement load for zombies, but trying to get the same POI over effective range - out of 2 different rifles.

That might not be a realistic goal. Most of this ammo will go towards killing soda cans & whatnot at 50M so as it performs today it will meet that requirement. It'll plink fine.

I'm searching for at least a 300M range near me though. My hope was to not have to re-zero based on ammo if I'm shooting at something like a B27 at a longer range. If the zombies do happen to rise, I don't want to have to remember my "zombie zero" or to readjust to it.

What I have found is that the 20" is grouping tighter for me regardless of ammo. So maybe I'll stick with it & leave the 16" for times i don't care as much about precision. The 16" has a Shaw barrel with at least 5k rounds - probably more - so it may be showing its age/wear.

Hummer70
January 1, 2012, 10:55 PM
Your variations are completely understandable but there is far more going on than you realize and making them "mate" is not likely to happen. To be taken into consideration are things such as:

1. The barrels you are using I suspect are not milspec which means they were not purchased on a gov't contract and inspected by gov't inspectors. There is an old saying that if it looks like a duck, quacks like a duck and walks like a duck it must be a duck.

With ARs just because it looks like a M16, sounds l like a M16 and works like a M16 doesn't mean you have anywhere near the same rifle endurance wise as the M16. As some state M4orgery or M4 wannabees and the description can also be applied to M16A2 wannabees. 95% of the parts available for these will not be the military drawings for those parts nor the endurance/corrosion, wear, reliability etc of the M16.

2.As well the bullets you are buying in all probability won't meet the gov't drawings either. Next chances are your primers won't either and I assume there is no mouth lacquer on your ammo.



3. The bore (land and groove) dimensions are not identical as after market barrels don't have to meet such. If your check cleared their bank it passed the manufacturers inspection standards.

4. Your standard deviation on you loads are very poor and there may be many reasons for this. You are looking for SD of 10 or less for top quality loads.

5. The 16" barrel and 20" barrel even if identical are not going to give same velocity as you have different barrel times.(amount of time bullet has to react to the pressure as it travels forward). In short the barrel the higher the velocity.

6. Different times in barrel equates to different barrel movements not only from velocity but from differing weights. Shorter barrels tend to give more muzzle movement when fired. Shoot a 18" 12 ga and a 30" 12 gage with same shells and you will quickly determine the shorter barrel appears to give more kick and more movement off the target.

7. If you are not using a scope on both rifles the sight acquisition is not as good on the shorter sight radius. Very few folks can focus on the short sights well.

8. The acceptance accuracy on both the M16, M16A1, M16A2 and the M4 are all 4.5" at 100 yards and rejection is 7.2" at 100 yards shall not be exceeded in a specified number of rounds fired at a specific schedule with a control lot of ammo.

9. Many ball propellants are highly erosive on barrels and thusly not all ball propellant is on the gov't Qualified Products List QPL for small arms ammo. The semi automatic loaders generally require ball propellants to be used and the selection of the wrong propellant and well cut your barrel life in half.

In short you are looking for the end of the rainbow at night.

CMV
January 1, 2012, 11:47 PM
Are my std deviations really bad? I thought 1% of fps was considered "decent".

Anyway, for the 10 shot string today out of the 16" the low was 2793, high was 2858, avg was 2834, & std dev was 22.1 (not 28.1 - typo above after looking at spreadsheet again). That's a 65 fps extreme spread - should I be seeing better?

2858 2848 2804 2834 2822 2846 2854 2793 2827 2852

Will see with tomorrow's session. I just loaded for it. Every case was measured & is within .002, every projectile weighed is within .2gr (all read the same & scale has .1 accuracy), and every charge was weighed twice & within .2 gr. I doubt I'll see much better performance though because other than weighing projectiles and double weighing every charge that's pretty much where I am normally.

Also did a sample of 6 each with -.0025 case length and +.0025 case length to see if 5 thou makes any difference. For those, the charges were trickled to dead nuts so maybe they'll show something better assuming 6 is enough of a sample for std dev to mean anything. But I'd say those 2 strings are going to be the best I can do with the equipment I have since everything I can control was measured as precisely as I'm able.

NeuseRvrRat
January 1, 2012, 11:51 PM
I expected the velocity to be lower, but assumed I'd get the same POI results.

i think you need to read up on ballistics

CMV
January 2, 2012, 12:36 AM
How does reading up on ballistics help me?

In rifle #1 M193 hits a target in a certain place at 50 yds and a certain place at 100 yds. My load hits the target at those same places at both distances although it has less velocity.

Rifle #2 (with the shorter barrel so I expected lower velocity from both M193 and my loads) M193 hits a target in a certain place at 50 yds and a certain place at 100 yds. My load hits the target at different (lower) places.

Considering both rifles are similar with the exception of barrel length and outer profile I thought my load would match the 50 & 100 yard performance in rifle #2 as it does in rifle #1. If that's a really poor assumption to make, sorry.

Striker Fired
January 2, 2012, 12:56 AM
The slower the bullet is traveling the longer it takes to reach a certain range.The longer a bullet is in flight to that range,the longer gravity imparts its evil grip on the bullet,thus the bullet strikes lower.The longer the range,the larger the pull.At 300yrds you will have a drastic difference in impact height because of that 200fps difference at the muzzle.

helotaxi
January 2, 2012, 01:15 AM
1. The barrels you are using I suspect are not milspec which means they were not purchased on a gov't contract and inspected by gov't inspectors. There is an old saying that if it looks like a duck, quacks like a duck and walks like a duck it must be a duck.

With ARs just because it looks like a M16, sounds l like a M16 and works like a M16 doesn't mean you have anywhere near the same rifle endurance wise as the M16. As some state M4orgery or M4 wannabees and the description can also be applied to M16A2 wannabees. 95% of the parts available for these will not be the military drawings for those parts nor the endurance/corrosion, wear, reliability etc of the M16.Totally irrelevant to the discussion, but getting a quality 20" barrel isn't difficult or expensive.

2.As well the bullets you are buying in all probability won't meet the gov't drawings either. Next chances are your primers won't either and I assume there is no mouth lacquer on your ammo.Again, relevance?

3. The bore (land and groove) dimensions are not identical as after market barrels don't have to meet such. If your check cleared their bank it passed the manufacturers inspection standards.without knowing what barrels he's using and what the QC limits are for that company, you can't make any kind of judgement as to the quality or tolerance of the bore. Even gov't contract supplied barrels have tolerances and are not all exactly the same. All the same, irrelevant.

4. Your standard deviation on you loads are very poor and there may be many reasons for this. You are looking for SD of 10 or less for top quality loads.His SD isn't that bad. Better than average, actually. I think that if you were to test a lot of mil-spec ammo, you'd find SD figures worse than that. Again, that isn't really relevant.

5. The 16" barrel and 20" barrel even if identical are not going to give same velocity as you have different barrel times.(amount of time bullet has to react to the pressure as it travels forward). In short the barrel the higher the velocity.He stated as much.

6. Different times in barrel equates to different barrel movements not only from velocity but from differing weights. Shorter barrels tend to give more muzzle movement when fired. Shoot a 18" 12 ga and a 30" 12 gage with same shells and you will quickly determine the shorter barrel appears to give more kick and more movement off the target.This is totally off base. The shotgun analogy doesn't work since all you're demonstrating is that a longer barreled shotgun has more weight out front and is thus less likely to exhibit a lot of muzzle climb. In reality, with the longer barrel, and the longer barrel time, the muzzle has climbed more from recoil before the shot leaves the barrel. With a rifle, especially an AR where the stock in inline with the bore and where MV is at least twice that of the shotgun, muzzle climb isn't as much of an issue WRT to POI. What matters more with precision is the harmonics of the barrel. The barrel flexes as the pressure wave from the shot travels down it. For best accuracy, you want to match MV and pressure to the flex of the barrel and time it consistently. The shorter barrel actually flexes less because it is more rigid. However, we're not really concerned about the different amount of flex between a 16" and 20" barrel because we're concerned with each rifle individually.

7. If you are not using a scope on both rifles the sight acquisition is not as good on the shorter sight radius. Very few folks can focus on the short sights well.Again, not relevant, as long as he's consistent with each rifle, that's all that matters.

8. The acceptance accuracy on both the M16, M16A1, M16A2 and the M4 are all 4.5" at 100 yards and rejection is 7.2" at 100 yards shall not be exceeded in a specified number of rounds fired at a specific schedule with a control lot of ammo.So?

9. Many ball propellants are highly erosive on barrels and thusly not all ball propellant is on the gov't Qualified Products List QPL for small arms ammo. The semi automatic loaders generally require ball propellants to be used and the selection of the wrong propellant and well cut your barrel life in half.Rate of fire and barrel heating has proven more determinant of barrel life than the type of powder used. With high rates of fire and extended strings of high rate firing, the power begins to matter. For a normal civilian shooter firing aimed shots with a semi-auto and not doing repeated mag dumps, this really isn't an issue.

In short you are looking for the end of the rainbow at night.I agree that he's chasing a bit of a pipe dream, but not for the reasons that you list.

mtrmn
January 2, 2012, 01:03 PM
+1 Helotaxi
Whether the OP's gun meets milspec is totally irrelevant.
Projectiles? maybe.
He will have to duplicate the ballistics of the .mil ammo he's using as a basis for his question in order to come anywhere close to the same results on target, if then.


His SD's are OK, I tried some .308 Fed Gold Medal Match once and had SD's higher than that but it still had the same good results you'd expect on paper. Too much attention to one detail and you'll overlook the 800lb gorilla in the room. Like all the other dimensions of this mystery we call ballistics.

If the bullets leave the barrel at the bottom of the barrel "flex" (for lack of a better word-help me out here) rather than the top of the "flex" cycle, that could account for low POI. Even without the obvious lower velocity of his reloads compared to the factory ammo.
The loads will have to be tailored for his specific rifle to match the performance of a factory round, and the odds of it doing the same in another gun are very doubtful.

wanderinwalker
January 2, 2012, 01:21 PM
CMV,

You've received lots of good advice above. Now I have a question for you: what kinds of sights do you have on the rifles?

I ask because the standard A2 sights are very repeatable and reliable in their adjustments for the most part. The solution to your "problem" is as easy as writing down the zero adjustment for load in A and rifle A, and load B in rifle A. When you switch, just reset your zero to the correct load. Competition shooters do this all the time, it makes you understand why keeping a log-book is helpful. I have (or have had) zeroes for 52gr, 69gr, 77gr and 80gr bullets for the same range and rifle before, and just set the sights according to what was going in the chamber.

The other thing is, if you want your ammo to match the drop tables of XM-193, you'll have to get to the same velocity with the same bullet. Though FWIW, I don't even drive 52gr bullets over 3000-fps in a 20" barrel with my AR loads. And there are much better bullets than 55gr ball for use past 200 yards.

CMV
January 2, 2012, 01:33 PM
The 20" is A2 configuration with standard iron sights. It also has a 4x20 carry handle scope which works pretty well out to 100 yds.

The 16" is an M4gery and typically has an Aimpoint Comp M2, USGI rear flip up sight, and fixed FSB. Right now it has a 3x9 scope in place of the Aimpoint.

In the near future the 20" is getting switched to a flattop upper receiver, FF tube, low gas block, and possibly a 22-24" varmint/target barrel although the 20" Bushmaster HBAR does pretty well for what I do. A lot of it's upgrades will depend on if I'm able to find a much longer range to shoot nearby.

The 16" will go back to it's Aimpoint and BUIS after I'm done playing with the loads.

popper
January 2, 2012, 01:50 PM
CMV ; from loading manuals - +50 fps / inch barrel length. So a 4" difference = 200fps. Very close to what you show. No, you won't get there. load em different and mark them or change the sights for the load, or just remember the compensation for the load an sights.

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