Range Report 1st round and last round fliers?

[krink85]

I recently purchased a DPMS LR308 used form a gun shop. I have no clue what happened with the gun before me but after puttign 100 or so rounds down the tube I have noticed a couple things. First its alot eaiser to shoot more with a semi auto than bolt action

, second I need to remember to tighten the scope rings all the way before I shoot

(this was done before I was havign problems and fixed), third and most important one the first round and the last round shot are fliers. They are not half an inch from the group but 2-3 inches. 3 round groups were pissing me off, so I started 4 and 5 round groups. the middle shots were shooting under an inch. I was shooting prone off a pack. It was only at 100 yards with the wind at my back @8-10 mph. I was shooting FGMM 168s 1-10 twist 18 barrel w/JP brake. Scope is a 10x SS. I think I have the who,what,where,and when now all i need is the why. Other than military this is the first AR I have shot for precision. Any help would be helpfull. Thanks in advance.

Rink

 

[The Mechanic]

Re: 1st round and last round fliers?

This is just a guess but, first round flier is more than likely bad position try some dry fire and NPA before first round. Last round may just be as LowLight has explained before typical of a semi's last round having a different recoil impulse. This is all a guess based on little info.

 

[psinclair]

Re: 1st round and last round fliers?

what is the trigger like?

good triggers solve a lot of problems.

 

[Bradley]

Re: 1st round and last round fliers?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: The Mechanic</div><div class="ubbcode-body">This is just a guess but, first round flier is more than likely bad position try some dry fire and NPA before first round. Last round may just be as LowLight has explained before typical of a semi's last round having a different recoil impulse. This is all a guess based on little info. </div></div>

+1

Also, unlike the rest of the rounds in an semi-auto, the first round is loaded manually and the bolt may not lock up as tight as it does when the gun is loading itself.

 

[krink85]

Re: 1st round and last round fliers?

Its a JP trigger. Red springs not sure of the weight.

I make an attempt to hit the bolt release every time but I will do some research on the manual close and what not.

Also I will be dry firing and paying attention more to my body positions.

 

[Sig685]

Re: 1st round and last round fliers?

As Sinister explained later, the last round syndrome in an AR-10 (and supposedly in an AR-15) is due to the bolt stop pressing on the bolt; it has nothing to do with the "different recoils".

With that in mind, for a 5 shot group, you should load 7 cartridges. Shoot the first one on another target, then shoot your 5 shot group and either eject the last round or shoot it in the other target along with the first round.

 

[sinister]

Re: 1st round and last round fliers?

Aw, man -- that's cheatin'!

The group's the group the way you'll deploy the weapon.

 

[Sig685]

Re: 1st round and last round fliers?

Sinister, I'm just trying to help the poor man figure out a good way that he can produce a "defensible" 5-shot group.

My groups are 15 or 20 rounds at a minimum of 300 yards. Anything less than or closer than that is cheatin' in my book.

One day, I hope to shoot sub-moa "all day long," if "I do my part." Came close last match with a 199-7 @ 300 on the FC. (Shot 17 was a 9. I must have sneezed or something.)

 

[sinister]

Re: 1st round and last round fliers?

Happens to all of us!

 

[Sig685]

Re: 1st round and last round fliers?

Yeah, maybe I'm allergic to brass or gunpowder. I'll try a noseplug or a full face mask. Nah, you'd call that cheatin' also.

 

[doc76251]

Re: 1st round and last round fliers?

Try swapping mags around. I had the same issues with my M1A back in the day. I ran about 10 magazines before I found the 3 that I used across the course with the same POI as the "pull and let go" magazine.

Cheers,

Doc

 

[Wil]

Re: 1st round and last round fliers?

I would figure the bullet to have cleared the muzzle before the recoil impulse hits...

hmm... Interesting thoughts

 

[The Mechanic]

Re: 1st round and last round fliers?

Frank had a big discussion about it a few months back that is why I referenced it. When I said different recoil impulse I am talking about the entire recoil and its effect. do a search and you can see what he said if ya' don't believe me Sig.

 

[The King]

Re: 1st round and last round fliers?

I would agree that the last round is a combination of issues - 1, the bolt stop is now in play.

You can eliminate this variable by eliminating the bolt stop. No joke. Goodbye.

2, many semi's do not have any contact with the bottom of the bolt when there are no cartridges in the magazine. So an upwards pressure that was there is no longer in evidence. This can be eliminated through loading more rounds than will be fired.

Some guns throw the last flier to roughly the same spot. My M14 did this. It was always +1 MOA up and 1/4 MOA right (group center). You can make a group of the flyers and then hold over for the last round to get it to land right.

 

[McCrazy]

Re: 1st round and last round fliers?

Krink- check out this thread: http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=980671&page=1

It is the one others have already referred to in this thread. Lots of guesses as to why semi-autos group a bit different than bolts but not much for solid facts. Still though, worth the read to get an idea of what is causing your issues.