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Gunsmithing FN SPR A3G/ Bolt lift on dry fire

J

justinblake

Private
Minuteman
May 31, 2011
23
0
44
Texas, USA
#1
Let me start by saying I'm new to long range and this forum. Thanks for any suggestions or opinions.

This rifle is factory, and has approximately 300 rounds down the tube. I have only fed her FGMM 168 and APPLIED BALLISTICS 175. I have been able to produced some pretty decent 3shot/100yd groups in the neighborhood of .35 MOA. Out to 600ish about .6MOA 5shots. 1000yds around 1MOA 5shots w/175s. Normally i just clean the actions after a day at the range, maybe a wet patch or two then dry patches every 20-30 rounds. I just recently used a nylon brush, wet dry patches on the bore til she was CLEAN!!! After 10 -15 rounds it was all i could do to shoot .75 to 1MOA. Strings were straight vertical. My cold bore shots were 1MOA high at all ranges, and every other shot of the string was as should be in respect to elevation. Horizontally sucked, but could've been me as well.

Because of this i started really looking the rifle over. I noticed the bolt handle was touching the stock in its recess not allowing the handle to seat against the action... no problem a Dremel took care of that. And I discovered the rear action screw had backed off, I'm guessing, to 30 in/lbs. The front was at 50 in/lbs so I tightened the rear to 50.

Shot it again, same group sizes but the cold bore shot dropped back down with the others. So I tried some dry fire shots to see if I was manipulating the trigger one way or the other. This is when I noticed the bolt handle would jump up about a half inch on the dry fire. I chamber a fired casing w/primer and it still jumps, but only 1/8 to 1/4 inch.

What to do? I would rather not ship my rifle off to FNH only to have it returned AFTER deer season! I could leave it with a gunsmith in the Austin/ Houston area but don't know any. I would only leave it with the best in those areas but then I'm sure it would be there for awhile too.

Is this common with pre 64 m70 actions, Is there an easy fix?


 
#4
Re: FN SPR A3G/ Bolt lift on dry fire

They never got below .75MOA. I figured 10-15 rounds would be plenty to re-season the bore. I'm into it about 60 rounds since that cleaning and no better. I know its a chrome-lined bore but it shouldn't take that long should it?
 
#5
Re: FN SPR A3G/ Bolt lift on dry fire

Same lot # on the ammo as you were shooting before?

I would expect it to take a few rounds down the tube before the groups returned but 60 is a lot more than I would expect. Have you double checked your scope and mounting systems for tightness?
 
#6
Re: FN SPR A3G/ Bolt lift on dry fire

I have checked everything in the mounting except for the one piece pic base. Every thing was good. I only have two lots of FGMM and they both shot good before. The A.B. is all the same lot. When cleaning I only pull from breech to muzzle, no bore guide, Dewey rod. I didn't notice anything unusual as far as tight spots and I'm very careful entering the muzzle so I don't think I damaged the crown.
 
#7
Re: FN SPR A3G/ Bolt lift on dry fire

Hmmm,

Double check the chamber and bolt lug area for any debris that may have come off your mop or patch/brush.

Other than that I would start experimenting with torque working up to 65 pounds. Remember not to do all torque at once but work up in stages on the front and rear action screws and make sure the rifle is fully seated back against the lug bedding.
 
#9
Re: FN SPR A3G/ Bolt lift on dry fire

Will do tomorrow and I'll post the outcome. As far as the bolt jumping up should I be concerned. I will check to see if it jumps after a live round also. Something I just thought about... the firing pin has always struck very slightly off center but is consistent.

Thanks
 
#10
Re: FN SPR A3G/ Bolt lift on dry fire

The jump is probably due to the spring torquing the firing pin and retainer around as it is released from the compressed state. The grouping is probably not related. I'd suspect 1...technique, 2. Bedding.
 
#11
Re: FN SPR A3G/ Bolt lift on dry fire

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 308er</div><div class="ubbcode-body"> As far as the bolt jumping up should I be concerned. </div></div>

Just checked, both of mine jump.
 
#12
Re: FN SPR A3G/ Bolt lift on dry fire

Nothing to worry about. With an empty chamber, there's no headspace; nothing to seat the bolt lugs. If you try it with a piece of spent brass it probably won't happen.

The impact shift was probably due to your cleaning it. Stay out of the bore on these guns unless it's not shooting properly. I don't clean mine but every 7-800 rounds or so, if that.

Mine takes about 20 rounds to foul back into the exact same POI after a thorough cleaning.

If you cleaned it every time you shot it, and you shoot 60 rounds per range trip, then 1/3 of the rifle's barrel life will be spent on re-fouling the tube. 1/3 of your ammo expense becomes waste.

For what it's worth. Some may believe differently and I respect that.


--Fargo007
 
#13
Re: FN SPR A3G/ Bolt lift on dry fire

On an empty chamber I don't own a bolt rifle that doesn't exhibit some sort of jump.

With a piece of spent brass the only one that jumps is the bone stock factory gun that is on the pile of projects I have coming up. It has many more indicators that it needs some work as well.

This includes a UGSW 911 and a BigHorn Arms receiver as well. Both of those guns are continually in the 3-4's with "screamer groups" being in the 2's.

As Fargo already stated, over cleaning is the bane of a barrel's existence. All of my rifles do not get cleaned until I'm either not going to shoot them for quite a while (there's a couple sentimental pieces that are this way) or the oft used precision rigs get cleaned when the groups open up to 1.5x-2x's normal size.
 
#14
Re: FN SPR A3G/ Bolt lift on dry fire

Okay, I tried alot of your suggestions, no debris in the action/lug area, took off my rings and scope and the base seemed okay.

I went to the 100yd line and re-sighted...SAME results. I worked my way up slowly torquing the action screws from 50in/lbs and my groups opened up wider with every change. So I went down with my torque and the groups started getting smaller. I settled on 45in/lbs because my 5shot groups started hammering .5MOA with one that measured 5/16" center to center of course.(My personal best 5shot to date) She got so consistent I easily called my misses.

Some of this could be that I really took my time to try and make myself consistent from shot to shot. On my smallest groups I single loaded the chamber (?).

Side note I tried Hornady Superformance Match 168Amax... My gun did not like these at all.
 
#16
Re: FN SPR A3G/ Bolt lift on dry fire

I have a FN A3-G.....Bob @ FN told me, that the FN A3-G was built around the 168gr. FGMM ammo!
It shoots sub MOA all day!

FYI.......They also told me, that they torque @ 65in/lbs.
On the A3-G.

LOBO 151
 
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