Gunsmithing Receiver floating?

[wallace11bravo]

Just got my slightly used GAP rock barreled action today (thanks again i_rep). I scurried home to the man cave and went to work installing it in a McCree R700 SA chassis.

I got it in, torqued to 65. And inspected it. I noticed a gap between the receiver and chassis. The only real difference between this action and the one previous is the BO recoil lug. To be completely honest, the previous one may have had this gap as well, and I just never noticed. There is no detectable play or stress. The right side has a gap just big enough to get a business card in there, the other side is just big enough to get a peice of notebook paper.

Wanted to see what you guys think. Is this a big problem, or not really a problem at all? If it is a problem, what are my options to correct?

I'll be giving McCree a call tomorrow to see what they think.



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[wnroscoe]

Re: Receiver floating?

V-blocks fore and aft? That would explain the air gap.

 

[wallace11bravo]

Re: Receiver floating?

No V-blocks. I took it apart and put it back together. Is the BO lug longer than a factory R700? That is the only thing I could point to that is causing this.

I put some grease on the bedding, and put the receiver on and took it back off to see if any would transfer. It did not.

 

[wnroscoe]

Re: Receiver floating?

The BO lug could be too long. In AI chassis's this is usually the issue. I mil the lugs down (shorten them) and open the front of the recoil lug pocket.

 

[wallace11bravo]

Re: Receiver floating?

Got ya. I was figuring as much. The pocket is wide enough, just not deep enough. If you don't mind me asking, how much would this little bit of milling cost me, typically?

 

[wnroscoe]

Re: Receiver floating?

Should be minimal, shipping would/should be the most expensive part of it.

It's simpe enough that a local high quality machine shop could do it provided you were there the entire time with the rifle. I know the BATF says that if working on firearms for profit the business will have an FFL so, just use your best judgement. If you know someone with a mil it's a 5 minute job at best.

 

[Bill Larson]

Re: Receiver floating?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wallace11bravo</div><div class="ubbcode-body">Got ya. I was figuring as much. The pocket is wide enough, just not deep enough. If you don't mind me asking, how much would this little bit of milling cost me, typically? </div></div>
Do you own a file..................????
bill larson

 

[9H_Cracka]

Re: Receiver floating?

The side of the receiver appears to be running parallel with the stock. I'm not convinced you have any type of problem at all there. If the lug were not allowing the front receiver ring to bottom out in the stock, the side of the receiver would be at an angle.

Use your dial caliper to measure how much the lug hangs down from the front receiver ring, then measure the depth of the lug recess relative to where the front receiver ring will contact the stock at the edge of the lug recess.

This will tell you if the lug is contacting the bottom of the recess.

 

[Trigger Monkey]

Re: Receiver floating?

How old is the stock?

I had a similar issue with a McRee Gen5 that I bought through US Tactical Supply. My issue was that the recoil lug slot wasn't deep enough and it was bottoming out when I torqued the action down. I didn't really notice it at the receiver area but the barrel was sitting up noticeably higher in the barrel channel. A good way to tell if the slot isn't deep enough is to remove the barreled action and look down at the recoil lug slot. If there appears to be a small step going from the forend to the recoil lug area, your BO lug is bottoming out. If it looks like a smooth transition then you're fine. I recommend giving Scott a call and talking with him but be careful it's easy to blow 45 minutes on the phone with him talking about shooting in general. When I had my issue he told me to just send in my center section and he'd send me a new one that was cut deeper for the taller lugs.

 

[shrompman420]

Re: Receiver floating?

i kind of like pickin his brain, so i dont mind blowing the time, he called me to talk about my prs issues. he knows his stuff imo.
got a long and short action g5 ar folder. long as over sized lug short is factory. just looked at mine and they seem to be seated down with no gap. hope it helps.

 

[former naval person]

Re: Receiver floating?

Put a pea sized lump of clay down in the recess, lube the bottom of the lug and torque her down. Remove and inspect. You'll be able to tell if it is bottoming out. JMHO

 

[wallace11bravo]

Re: Receiver floating?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bill Larson</div><div class="ubbcode-body">
Do you own a file..................????
bill larson </div></div>

It is a gen 5.

I did a few more tests to ensure that I had the problem identified correctly. I used white lithium grease with blue food coloring and put some on the bottom of the receiver and the recoil lug. I installed and removed the chassis, and indeed, the recoil lug was "holding up" the front end of the receiver, as there was grease transferred to the chassis from the lug and towards the rear of the action, but none for the front ~1/2 of the receiver. I installed it once more, and took the stalk apart just in front of magazine well (4 machine bolts) and it confirmed my suspicions as well.

Called up MP, they confirmed that they had seen this problem before, and recommended shaving about 90/1000 off the bottom of the recoil lug.

After much personal deliberation, I decided to attempt this myself. I figured absolute worst case scenario, I would have to purchase a new RL and have it installed.

I placed the receiver upside down in the vise, and leveled it. I used dial calipers and some ingenuity to track my progress, and the level to ensure I wouldn't end up grinding it down at an angle, and that the surface was even. Dremel, dremel, dremel, and after about 20 minutes of careful work, I was satisfied with the amount removed and the squareness and smoothness of the lug. I used a fine flat file and fine dremel bit to finish it out, ream, and bevel the edges slightly.

I used a bit of Oxpho-blue to protect it, and other than the slightly mismatched finish, I would say I did a hell of a job. Nice and smooth, no burrs, evenly tapered, appears perfectly squared up by any methods I have of measuring. It now rests in the chassis properly, with about 15/1000 clearance from the bottom of the recoil lug pocket. I did the blue test again, and it confirmed my conclusion.

Thanks everyone for the advise and ideas, sorry for neglecting this thread.