4" groups at 50 yards is not acceptable

jimbobborg · Jun 6, 2019

I picked up some Frontier 62gr 5.56 ammunition and re-zeroed my two 3-gun rifles. My lightweight build was off by quite a bit from its initial zero made with 55gr FMJs, and I was getting 4" groups at 50 yards. ??? I tried my old 3-gun rifle, an was getting clover leaves. I can see why I couldn't hit squat at the last two matches I used the lightweight gun on.

When I sighted in the lightweight build with 55gr ammunition, I was getting 2" groups at 100 yards. The barrel is a 1 in 8 twist, so it should be shooting better with heavier bullets. I'm going to try some 75 gr versions of the Frontier ammunition when I can find it.

Why am I bringing this up? I assumed that things were close enough between the two rounds that I didn't need to check zero and do testing. I was wrong. Always check.

davsco · Jun 6, 2019

Yeah there's enough stress and weird positions going on at a match, that close enough, isn't. Folks have to have their dope /poa/ poi down from 0 to the furthest distance they're shooting.

Squaregrouper · Jun 6, 2019

Last Friday at AGC's 200yd range, a guy had an overcharged .223 by Frontier. It blew out the primer, ripped the case upon extraction and left residue all over the guy and his magazine. Fortunately he was wearing eye protection.

Qbeam · Jun 6, 2019

What are the specs for both guns?

Q

Racer Doug14 · Jun 6, 2019

Is that 62gr a lead core? Or a steel "ss109" type?

dist1646 · Jun 6, 2019

With groups that large at short distance, I would be taking a look at the barrel.

jimbobborg · Jun 6, 2019

Both guns are 1 in 8 twist. One has a Faxon 14.5" pencil barrel the other has a DPMS 18" SPR profile barrel. The Faxon barrel was pretty accurate with everything else I've used prior to this.

All bullets used are lead core. None of my ranges allows steel core.

jimbobborg · Jun 6, 2019

dist1646 said:
With groups that large at short distance, I would be taking a look at the barrel.

I didn't have time to look last night, I'll check today when I get home.

davsco · Jun 6, 2019

maybe scope came loose or something, that is a gi-normous group. plus some barrels just like certain ammo. maybe try the 'old' ammo again just for yucks.

Qbeam · Jun 6, 2019

Was the 4" group at the beginning or end of the shooting period? Wondering if the barrel profile, and length of shooting may have opened the groups. Could be the ammo/barrel as well.

Q

danb · Jun 6, 2019

dist1646 said:
With groups that large at short distance, I would be taking a look at the barrel.

Or the scope, mounts, etc. Things do sometimes come loose.

I use 62 and 55gr virtually interchangeably in my Faxon heavy barrel. The POI shifts, the 62 gr is midly more accurate, but you would have to go out to 200yds for most people to see the diff. Definitely not 4" at 50 yds diff.

jimbobborg · Jun 6, 2019

davsco said:
maybe scope came loose or something, that is a gi-normous group. plus some barrels just like certain ammo. maybe try the 'old' ammo again just for yucks.

Funny you should mention that. I had just tightened up all of the screws on both rifles with my new Wheeler Fat Wrench the night before. One screw needed tightening, the rest were in spec.

Qbeam said:
Was the 4" group at the beginning or end of the shooting period? Wondering if the barrel profile, and length of shooting may have opened the groups. Could be the ammo/barrel as well.

Q

I shot 20 rounds total out of the shorter rifle. I adjusted the scope after every third round, so barrel didn't get too hot.

onedash · Jun 6, 2019

I've noticed some massive shifts with ammo changes, Far more than I would have imagined possible. All shot excellent groups but each group was no where near each other. All in 308 with similar but usually not identical bullet weights. Like going from 165,168 or 175 gr at 50 yards you would think they would all be pretty damn close. But I think there was about a 6" spread between them.

Qbeam · Jun 6, 2019

jimbobborg said:
Funny you should mention that. I had just tightened up all of the screws on both rifles with my new Wheeler Fat Wrench the night before. One screw needed tightening, the rest were in spec.

I shot 20 rounds total out of the shorter rifle. I adjusted the scope after every third round, so barrel didn't get too hot.

Adjusted the scope for Point Of Impact (POI) or Point of Aim (POA)? One is for optic correction, the other is for moving the grouping (box test).

Q

dist1646 · Jun 6, 2019

danb said:
Or the scope, mounts, etc. Things do sometimes come loose.

I use 62 and 55gr virtually interchangeably in my Faxon heavy barrel. The POI shifts, the 62 gr is midly more accurate, but you would have to go out to 200yds for most people to see the diff. Definitely not 4" at 50 yds diff.

Good point and certainly something to look at. Loose mount, scope failure, etc. does happen.

Rab1515 · Jun 6, 2019

Check the crown on the barrel and/or muzzle device.

Qbeam · Jun 6, 2019

Rab1515 said:
Check the crown on the barrel and/or muzzle device.

Wouldn't this affect all the rounds, regardless of weight?

Q

smokey · Jun 6, 2019

barrel nut torqued correctly?

jimbobborg · Jun 7, 2019

I cleaned the barrel and brake more thoroughly than usual. Not sure if that helped yet, I'll see if I can test it sooner rather than later. I'm shooting a 2-gun match this weekend, I'll be using my original 3-gun rifle until I can get this one sorted

Boats · Jun 7, 2019

Faxon makes some damn fine barrels. I have 3 and they are all stellar.

I have heard some reports about frontier ammo having very dodgy quality control, particularly with powder charge.

4" groups at 50 yards is not acceptable

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