I am just completing a build for a friend, and I have a question.
When charging the weapon, it feels ‘stiffer’, and not as smooth as my other ARs. I compared my others, including one that I built, and they all seem slide much smoother. Does it just need to be shot? Or is there a concern with the spring?
The upper is a BCM middy with BCM BCG. Lower is a Spikes with a G&R LPK, and it has a carbine buffer (spring and buffer from DSG Arms MAGPUL kit).
I think it varies by buffer tube and by spring. I’m using a Tactical Springs (blue) spring in a VLTOR buffer tube on an SBR carbine I built. I notice that there’s a distinct “dragging” noise from the spring/tube when I charge it. It works fine, however, so I ignore it.
Aftermarket receiver extensions often don’t have the smooth inner surface that a real Colt mil spec receiver does.
Has the weapon been lubed yet?
Different carriers feel different too. There’s a more drag on my BCM carrier, vs the stock S&W carrier.
The BCM is full auto so it’s heavier which would create more resistance while charging.
There are tolerances on bores and shafts and the ANSI/ISO standard is called limits and fits.
http://www.mitcalc.com/doc/tolerances/help/en/tolerancestxt.htm
No rifle will ever be exactly like another (we are talking absolutes here) because of tolerances. The materials have tolerances (% of alloys), and mating components have size & position tolerances.
There are also other factors besides size and they are called geometric tolerances.
http://www.efunda.com/designstandards/gdt/introduction.cfm
Straightness, run-out, concentricity, parallelism, position are some of the important geometric tolerances that affect our rifles.
I suspect that some of the top manufacturers of AR components have a fantastic set of machinists, programmers, and QC staff.
With all that being said, your newer build “feels” different than other rifles due to tolerances.
… those are some delicious pieces for a build and I’ll bet the rifle will shoot sweet!
Thanks for the replies guys. It does seem to be a “drag” in the carrier rather then the spring. Just seems a bit odd that all four of my ARs are very smooth, and this one is not. Yes, the weapon has been lubed.
We did shoot it a small amount last week, and other than not being sighted in, shot very well. Going to put several hundred rounds through her this week.
Break the gun down and check. In the gun I describe above, I had assumed it was bolt-catch drag, but breaking it down showed that the bolt carrier slid back and forth in the receiver smooth as butter. Compressing the buffer spring back and forth, however, duplicated the noise exactly.
I switched the buffer and spring from another build, and it seems to be slightly better. The one in there now is a Colt H buffer and spring. I noticed the spring I removed was a bit longer…seems a bit strange.
UPDATE: Ok, after switching parts back and forth, I have decided the main problem now is the receiver extension. So, while this may not impede the performance, I am not satisfied with this for the build, seeing as I have promised my friend a top tier AR. I will be changing out the tube for a BCM mil-spec one this week.
PS: it appears to me that the DSG Arms package deal, was not as good of a deal as I thought. The end plate was commercial, not mil spec as described, the spring was longer than the mil spec, and the tube grinds…
LMT’s rec ext is coated with a dry lube and very slick inside and out.
My BCM mil tube is nice but I don’t remember it being especially slippery inside, not rough or anything just not dry lube or such that I could tell.
There are such things as spray dry film lube available fwiw.
Also the end plate that came from them with mine was not exceptional, the visible edge had some roughness from crappy casting looked like, just like the no-name commercial tube had that was on there when I got the lower. YMMV, I’m going to find one somewhere from someone that is more attractive.
This stuff has worked well for me:
The Noveske QD endplate is very well-made. Maybe less important for you if you’re not looking for a sling swivel point, however.
I was eying them actually, I’ve also wanted to try an endplate sling attachment and see how it compares to the vertical slot on the CTR stock I’m using now.
The end plate was commercial, not mil spec as described
Receiver extension end plates are not broken down as commercial or mil spec. They are the same.
I saw that, I meant commercial as in “cheap crap made by a monkey”. 
the spring was longer than the mil spec, and the tube grinds…
Carbine spring spec is 10 1/16" to 11 1/4". What did you have?
Test fired this weapon today, and some issues with the bolt locking open on empty mag. Used a few different mags, and value box Federal, as well as Wolf. It was not a consistent problem, it was sporadic. Next range trip I will try more useful troubleshooting with a variety of mags, try different uppers, BCG, etc.
Anyways, does anyone think that the above mentioned receiver extension dragging could be enough of an issue to cause the bolt to not always lock open?
Also, this AR has a BAD lever, and I suppose that could be an issue as well. Thoughts?
Thanks again for all the input.
Did you happen to eyeball the upward movement of the bolt catch lever and see if it is engaging the face of the bolt high enough? I just learned this failure mode of out of spec parts on my first build. Mine was only just barely grabbing the locking lugs on the bolt at there lower tips with the bolt catch at full upward movement. Dremel fixed it till I order a better LPK.
Putting a few hundred rounds through an AR will smooth out operation and show wear points.
I highly recommend that anyone that builds a new gun test fires it in as “stock” configuration as possible before adding things like BAD levers and such. It greatly simplifies the troubleshooting process and gives the user a known baseline in case of future issues.
I agree 200%. We have seen numerous times here where personnel have added every Magpul cool guy accessory known to mankind only to have the weapon malfunction.
That doesn’t even include the dicking with buffers, springs, flash hiders and brakes, etc…