Accuracy of Semi-Auto Rifles


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Drakejake
May 24, 2006, 08:23 PM
The Mini 14 is supposed to be less accurate than the AR-15. The Mini may be fairly accurate for the first two or three shots, but once the barrel gets hot, the rifle starts spraying shots. Or so the story goes.

Today I shot a Mini 14 and a DPMS Lite with 16 inch medium thick barrel. The first couple of shots from each rifle were on target but after a few shots, the point of impact moved about four inches to the right, or to the lower right. My Mini with a homemade barrel stiffener attached to its pencil barrel (thinner than the one on the DPMS) seemed to move less far away from the aimed at spot. What gives? Do all semi-auto rifles when hot move shots off-target? Does a heavy barrel really keep shots on target? Is it OK if you have small groups which are nowhere near the spot you are shooting at? Does that make sense?

Next time I am going to take my K-31 out to the range for an accuracy test.

Thanks,

Drakejake

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Oldnamvet
May 24, 2006, 08:28 PM
Who told you that??:confused:
Also, precision is what you want. That is the grouping of all the shots together. Accuracy is how close you come to the bull of the target. Once you have the precision, the accuracy is just adjusting the sights. Then you will have both.

Drakejake
May 24, 2006, 08:46 PM
Are you saying that the scope should be readjusted after the barrel is hot?
The rifle will be off-target on the first few shots, right? What if the point of impact keeps shifting? (Sell the rifle or the scope?)

Thanks,


Drakejake

Lost Dutchman
May 24, 2006, 09:08 PM
He's talking about poi shift, and no, it's not to be expected. I've had two semi-auto rifles. The last one was an sl-7 with a 10x european sniper type scope. No point of impact shift, none, just great 1in and sub 1in groups every time. Those little rugers are good little rifles, reliable and virtually indistructable, not known for being accurate tho.

Drakejake
May 24, 2006, 09:41 PM
But AR-15 behaved the same way, so far as I could tell. I was using scopes from 50 yards, with a tripod, seated.

Drakejake

GoRon
May 24, 2006, 09:55 PM
4 inches!

You sure your scope mounts are tight.

My AR-15 barrel has been hot enough to take the skin off your arm and it still hit where the EOTech was pointed.

Dionysusigma
May 24, 2006, 09:58 PM
Depends on the rifle, I guess. Compare the accuracy of a Ruger M77 versus an Hk PSG-1.

Mannlicher
May 24, 2006, 10:10 PM
My experience does not match yours regarding inaccurate semi autos.

dwave
May 25, 2006, 12:31 AM
It is not limited to semi's, it just depends on the gun. My SKS keeps it's POI hot or cold, but my Mosin-Nagant bolt action moves to the left when it gets hot by about 1 inch @ 100 yards.

Onmilo
May 25, 2006, 12:32 AM
There was an ole' boy here in Illinois that went by the name 'Chief A.J.'.
I believe he passed on now, but anyway,
He could do things to the Mini-14 that would make the rifle shoot with the best of the comparable AR15 rifles.

When you compare a lightweight and basic AR-15 with a basic Mini-14 you will likely find they are very comparable in the ability to group shots about the same way.

I think the Mini-14 can be made to shoot just as well as a Match grade AR-15..
Ruger has never elected to bring the rifle to its full potential.

jd46561
May 25, 2006, 12:35 AM
Take that k31 to the range , your mini 14 will sit in the safe. :)

Drakejake
May 25, 2006, 12:43 AM
I am a clueless rifle novice, but I think the scopes are on tight. Thanks for all the comments.

Drakejake

goon
May 25, 2006, 01:03 AM
I think it has more to do with the profile and weight of the barrel than it does with whether or not it is a semiauto.
I have seen some semiauto rifles throw the first shot away from the rest of the group by a comparatively small amount. This doesn't seem to have as much to do with a cold barrel as much as it has to do with the first hand cycled round in the group. Some don't seem to do this. None of the rifles I have now seem to have this problem except for my 10/22. It is only about a half inch at 50 yards so I just shoot it and don't worry about it.
A bigger factor seems to be how thin the barrel is. I have owned a couple bolt action rifles that would punch a dime sized group at 100 yards with the first 3 or so rounds. My Savage Scout .308 did this. After three rounds my impacts would start to move up and right. I never shot it to see if this was self limiting but if it wasn't it would have worked its way clear off the target with a couple more rounds.

My AR has a heavy barrel on it. It doesn't have quite the pointability I would like but it does keep putting rounds at the same point of impact even when it is too hot to touch.

Just my experience. Your mileage may vary.

TX_RGR
May 25, 2006, 01:07 AM
Hope you dont mind the "butt-in" butt...

What is it about a bolt action that makes it more accurate than a semi rifle in general? I have a hard time getting my head around that one. Once the bullet is in the chamber, it's pretty much chamber and barrel the rest of the way. How does the action to rechamber a round affect accuracy? This may be one of those things that everyone already knows (or everyone but me), but I'd love to get the info on that one if you all dont mind sharing.

rockstar.esq
May 25, 2006, 01:46 AM
So the textbook reply as to why bolt's generally get the accuracy nod is that some semiautos have chambers that are cut a little looser to allow for more reliable functioning. Given that most semi auto bolts close under spring pressure it's easy to understand that as a spring encounters resistance it will apply differing amounts of pressure to the rear of the bolt. The bolt action has a person's arm driving the bus. Due to the ability to overcome chamber fouling (which happens after each shot), the bolt action generally seats itself to exactly the same place. Another reason that bolts are considered more accurate is that the powder charge and it's attending energy varies slightly from one cartridge to another. Even match ammo has velocity differentials. The semi autos use this energy to drive the loading mechanism and given that there will be slightly varying amounts of energy, there will be slightly different forces applied to the bolt. Whereas the bolt action is largely unaffected by such conditions. And finally the bolt action allows the barrel to be free floated from the reciever onward whereas the semiauto has a gas block that can add vibration to the barrels harmonics thus mucking up the accuracy. Just one guy's opinion I'm sure others will follow.

g56
May 25, 2006, 01:56 AM
A lot of times the groups will open up when the rifle gets hot, I recently had my AR groups open up quite a bit, I was mystified till I found the scope mount loose! Here's a group from my AR15 franken rifle.

http://www.pbase.com/wingman26/image/43513209.jpg

KC&97TA
May 25, 2006, 02:29 AM
you didn't give a distance? Most weaons don't start to change POI till they are really, really hot. I proved this one day by shooting a 5 shot group with a M16A4, then blew 14 rounds out on burst and then siteing back in for a 5 shot group on another target. This was at 100 yards, there wasn't much of a difference in the groups, a little more open.

5 rounds @ 25 yards with my M4 can be covered by a dime.

I've shot 10 round shot groups at 1000 yards with my NM AR-15 that were sub-moa, actually they were 7-1/2 inches and that was from the prone, not bench rested. From a bench rest the rifle will do 5", 5 shot groups @ 1000 yards. That's 1/2 moa @ 1000 yards, there's many bolt guns that can't do that.

Like those numbers? it's a Rock River Arms National Match Upper, 2 stage Geissele trigger and 77gr Sierra Match King Molly Coated ammo and I only bore snake it, never put a cleaning rod near it :neener:

How much do you want to pay to have an acurate semi auto? I got more than I want to admit stuck into the NM AR-15

JohnKSa
May 26, 2006, 12:53 AM
Some guns walk the POI when they get hot. Some don't.

It has to do with a lot of things, and being a semi-auto isn't one of those things.

All things being equal, a semi isn't as likely to be as accurate as a similar quality bolt because accuracy = consistency. There's a lot of stuff that moves around inside a semi-auto after each shot and there's not much that moves around in a bolt rifle. That means it's more likely that everything gets back in exactly the same place for each shot with the bolt and more consistency is good.

That said, I've seen some semi-autos that would shoot better than some bolts. As usual, we can only talk in generalities on subjects like this.

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