Bolt travel distance?

[Corey]

Finally got the last pieces of the puzzle and working on putting it together. I've read where bolt travel can be a problem and if it cycles too far, some internal parts can be broken in the lower. I have a New Frontier glock lower. How much further past the ejection port should the bolt travel? I've seen where people use quarters as spacers behind the spring. I'm guessing that's just to stop the rearward travel, but is there an optimum distance it should clear the port? Open just enough to clear it or go further?

[MikeRush]

The spacers/quarters are typically used to prevent damage to the bolt catch, if you have a functional LRBHO. In that case, the consensus is you want the bolt to travel just barely rearward of the point where you can engage the bolt stop, to prevent the bolt/buffer from having room to gain significant speed before hitting the catch in forward travel.

I will want a functional LRBHO next year, but I actually prefer the impulse of a lighter buffer with no spacer for increased travel. Quarters are cheap and you can tune to suit your personal preference. IIRC the New Frontier doesn't have LRBHO built into the lower. 

[Odessa Straight]

Mine is a PSA AR-15 lower with a Haun mag block for Colt type 32 round mags and a PSA 16 inch 9mm upper. It has a heavy buffer in a carbine length buffer tube.  I have read that the bolt hold back takes much stress as the bolt travels far past it before beginning to return to battery and then slamming into it under great inertia.  I used quarters (I think 12) to shorten the distance between the fully retracted bolt and the bolt hold open.  I kept adding quarters until there was just about 1/4 inch between the two with the bolt held firmly back.  I could get another quarter, or two in the stack, but 1/4 inch seems just right to me.  I've fired 1500 rounds since the quarters without any malfunctions and the bolt always locks back.  I've disassembled the bolt hold open latch and do not see any evidence of damage.  I know plastic spacers are made for this purpose, but I like the quarters.  The quarter stack is finely adjustable by addition or subtraction and if you're ever caught short on change to buy a cup of Joe on the way home from a match the $ is just a field strip away. 

Edited October 3, 2016 by Odessa Straight

[MarkCO]

I use a polymer spacer.  It is cut to give me about 1/4" of bolt travel past the bolt catch.  QC10 Glock9mm lower.

[Corey]

Sounds like I need to put a bolt catch on my lower to check this then, lol. I robbed a bunch of parts off an older build for this but didn't have a blot catch at the time. I figured, its going to have a flag in it or be in use so the need to lock it back wasn't astronomically high for me. 

[Chip3]

Colt lowers have the bolt catch on the lower. If you use a standard carbine length buffer you will get more than an 1" of over travel that hammers the catch and can lead to premature breakage. On the colt style you can use an extended buffer or spacer. You can buy or make your own spacer and close the gap down between the bolt face when fully retracted and the bolt catch.

Your glock style NFA lower is set up to work with their upper which is where they put their bolt catch. May want to call them and see if a bolt catch will work in the lower before you try installing one. Not sure if the lower bolt catch will hit the glock mag correctly and if you would need a standard AR bolt catch or extended colt 9mm. My guess would be they put it in the upper for a reason. They also sell an extended heavy buffer and a spacer. Neither is very expensive. You would only need one or the other. 

Edited October 4, 2016 by Chip3

[jrswanson1]

Maybe I'm missing something, but is there a 6-position buffer tube made for 9mm ARs?  For those who purchased a complete 9mm AR, is the tube shorter than a standard 5.56 tube?

[Patrick Scott]

If you dont care about the gun locking open on empty or if you have a lower that last-round-bolt-hold-open doesnt work in then tune with spacers/spring/buffer until you like the way the gun feels and tracks. If you do want it to lock open on empty then 1/8-1/4" past the bolt catch(its gun dependent).  I have no LRBHO and I like the way the gun feels and tracks with 130pf ammo, full bolt travel, 223 spring, H2(4.6oz) buffer. Out of all the different springs, buffers, and spacers I have tried, this seems to give me the least amount of dot movement. 

[Odessa Straight]

Reading the other posts about the bolt lock reminded me that I didn't mention that I do find that having a functioning bolt hold open is a good thing in USPSA matches.  Since my local club has started recognizing PCC division I've shot 4 USPSA matches and 3 CQB matches.  More than once I've blown my stage plan and taken more make-up shots than planned; anyway I've run dry and bolt lock saved time on the reload.  With the bolt locked back it's much easier to lock in a fresh fully loaded mag than if the bolt is forward.  I carry a downloaded mag just for any speed load (chamber loaded, bolt forward), but also carry a fully loaded mag for a bolt lock reload.  I also like locking my bolt back during ULSC to insert the flag safety.  This saves time the next time I'm making ready I just remove the flag safety without having to rack the bolt back first.I also have a carbine (MAC 10) with no bolt lock catch and just don't shoot USPSA matches with it mainly because I want the bolt hold open feature. 

Chip3 was spot on about those bolt travel measurements for my AR which is just a regular AR-15 lower and 9mm mag block with a 6 position stock carbine length buffer tube.  The quarters for spacer works great in my AR with 1/4 inch between the face of the bolt and the catch when the bolt is held firmly back.  The spacer did seem to help smooth out the cycling of the gun, but it never was harsh before the spacer.  It's a real treat to be able to follow the dot and actually be able to call your shots.  i like it so much that I got an identical red dot (Burris fastfire 3) to mount on a CZ 75 and shoot some Carry Optics, too

 

[Corey]

Locking back isn't much of a concern for me. Sounds like its time to get some ammo around and tune it up a bit. Going to have to be factory ammo for now as I don't reload 9mm, but that's going to change over the winter I'm guessing.

 

[Patrick Scott]

I shot my PCC this year with 147gr loads that make 130pf out of my CZ and run in the upper 140pf range out of my 16" PCC. One day after a match with played around with some 115gr Win white box and let me tell you the difference was huge. The WB ammo had a noticeable increase in recoil and dot movement, it was quite nasty. If you are stuck(for now) with factory ammo, try to run heavier subsonic stuff or factory loads geared to USPSA minor shooters. I recently did some testing of load that makes 130pf(reduced my Production load) out of the carbine and while the recoil reduction over my standard Production load was slightly noticeable Im not quite sure its worth having two different loads for the guns compared to one load for both divisions. 

[Les Snyder]

I recently switched from Precision Delta 147s to Bayou 135 coated...I had a couple of the coated bullets engage rifling to the point where clearing was a problem, so seated the next batch a little deeper.... had an interesting chronograph session..  loaded some 147s to the shorter dimension, and with the corresponding pressure jump, went from just over 900fps out of my G34  to 960,and 1250fps out the the carbine...dropped the powder charge .4grain for a compromise load for both divisions... settled on one load of about 130pf for the pistol and 144 for the carbine... seating depth does matter

 

FWIW: I run a much heavier bolt and buffer in my PCC with a .308 spring than most of you have reported

Les L747