Overlooked BCG components

[Iraqgunz]

Toolcraft does not make bolts. They make the carriers.

I would add my experience to the proposition that proper manufacturing, tolerances, and heat treatment are the most important. Both 8620 and 4140 were used early-on for bolts in the ARs development. Heck, the original Colt 601s had 6061 aluminum receivers and receiver extensions, and yet they are going strong. ArmaLite's modern AR-10 bolts are made from 8620, and I have over 25,000 rounds on one of them with nothing more than finish wear and the preventative maintenance extractor and ejector spring changes every 10,000 rounds. The springs were fine, but I change springs BEFORE there is a problem. I also have a 1959-production AR-10 made in Holland, and from my research contacts - I am the author of the recent book on the AR-10 from Collector Grade Publications - I discovered that the exact rifle I own was fired around 40,000 times in its 13 years in Mozambique, most of that fire in full-auto, and never had any part replaced, even springs. The bolts on those Dutch-produced AR-10s were 4140 at the very best, and were hard-chromed on all surfaces (even the firing pin retainer is chromed), and not even the bolt lugs, bolt face, or cam pin on this Portuguese AR-10 have any areas where the chrome has worn through, let alone cracked.

Toolcraft, if it has not been said here before, is a tier-1 builder. They have NAICS codes and produce BCGs for the military, and for various top-end OEM AR-makers. Either their 9310 or C158 bolts are excellent, and the C158 is their mil-spec one. Their carriers are also totally mil-spec, and their key staking jobs are tied with Colt with the best I have ever seen.

[AR-Tenner]

Ah, so that is why their bolts vary in materials sometimes.

[lysander]

I would add my experience to the proposition that proper manufacturing, tolerances, and heat treatment are the most important. Both 8620 and 4140 were used early-on for bolts in the ARs development. Heck, the original Colt 601s had 6061 aluminum receivers and receiver extensions, and yet they are going strong. ArmaLite's modern AR-10 bolts are made from 8620, and I have over 25,000 rounds on one of them with nothing more than finish wear and the preventative maintenance extractor and ejector spring changes every 10,000 rounds. The springs were fine, but I change springs BEFORE there is a problem. I also have a 1959-production AR-10 made in Holland, and from my research contacts - I am the author of the recent book on the AR-10 from Collector Grade Publications - I discovered that the exact rifle I own was fired around 40,000 times in its 13 years in Mozambique, most of that fire in full-auto, and never had any part replaced, even springs. The bolts on those Dutch-produced AR-10s were 4140 at the very best, and were hard-chromed on all surfaces (even the firing pin retainer is chromed), and not even the bolt lugs, bolt face, or cam pin on this Portuguese AR-10 have any areas where the chrome has worn through, let alone cracked.

Toolcraft, if it has not been said here before, is a tier-1 builder. They have NAICS codes and produce BCGs for the military, and for various top-end OEM AR-makers. Either their 9310 or C158 bolts are excellent, and the C158 is their mil-spec one. Their carriers are also totally mil-spec, and their key staking jobs are tied with Colt with the best I have ever seen.

Actually, theses were not hard-chrome plated, they were "Electrolized", a proprietary form of thin-dense chrome (TDC). There are some major differences between TDC and hard-chrome plating.

As to analogies between AR-10s and 15s, be careful. The geometry of the lugs is very different. AR-10 lugs are trapezoidal when viewed from the front whereas AR-15 lugs are rectangular. This has drastic implications on the stresses at the base of the lugs.

[AR-Tenner]

Actually, theses were not hard-chrome plated, they were "Electrolized", a proprietary form of thin-dense chrome (TDC). There are some major differences between TDC and hard-chrome plating.

As to analogies between AR-10s and 15s, be careful. The geometry of the lugs is very different. AR-10 lugs are trapezoidal when viewed from the front whereas AR-15 lugs are rectangular. This has drastic implications on the stresses at the base of the lugs.

That is a very good point about the AR-10's different geometry. The AR-15's bolt actually derived from the early iterations of the AR-10's bolt, which had thinner and completely-square lugs. The improvements done by the Dutch for the Portuguese-contract rifle, including the larger and differently-contoured bolt lugs was kept from ArmaLite-Fairchild by Artillerie Inrichtingen over their anger of the sale of the patents to Colt. It was the Portuguese bolt with its widened lugs that gave the AR-10 its reputation in military service for parts-invulnerability, and in all my research for the book, I never encountered a single instance or report of a broken Portuguese-contract bolt.

The modern AR-10 as made by ArmaLite was based on 1959 ArmaLite-Fairchild plans, and on studies of the improvements made for the Portuguese contract, and I have found that the even the finish on the lugs of my modern AR-10 bolts wears at a significantly-slower rate than that on even the highest-grade AR-15 bolts I use, despite the higher round count that my AR-10s have over my AR-15s. In the AR-15s I have recently upgraded to LMT enhanced bolts (in standard all-chrome toolcraft carriers) to try and achieve something like the longevity that I get from AR-10 parts.

However, even though the AR-10 design is easier on bolts than the AR-15, it still speaks well to the doctrine that proper heat-treatment, tolerances, and manufacturing standards are of paramount importance that an 8620 bolt can be going strong after 25,000 rounds, or that a 4140 bolt can still look and function like new after something like 40,000 rounds of mostly full-auto fire.

[MistWolf]

Be careful of the LMT enhanced bolts. They use two extractor springs but the springs on the bolt I got were underpowered right from the start. The springs aren't standard AR extractor springs, either.

[AR-Tenner]

Be careful of the LMT enhanced bolts. They use two extractor springs but the springs on the bolt I got were underpowered right from the start. The springs aren't standard AR extractor springs, either.

Thanks for the tip! I heard such reports, but decided to pull the trigger on the upgrade anyway. My experience with LMT being so good about customer service made me willing to take the risk, and I also already have 2 spare extractors (2 bolts in service in my 2 AR-15s) and 8 spare pairs of extractor springs, all at the proper length spec. I also keep 2 standard bolts and a carrier as spare for each rifle, but I am running the LMT Enhanced as my first-line bolts.

[Iraqgunz]

Based on what saw, if you take an ejector spring and cut it down approx. 1/3 it will be about the same exact size as the current extractor springs.

Be careful of the LMT enhanced bolts. They use two extractor springs but the springs on the bolt I got were underpowered right from the start. The springs aren't standard AR extractor springs, either.

[bruin]

Mistwolf, do you have a recent production E-bolt? I ask because I thought that this was an issue with the early ones and later corrected. You could also customize your extractor tension, as IG pointed out.

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[tom12.7]

While I can't speak for what LMT offers for their extractor springs, KAC has/had different color coded extractor springs with different tensions.
I have heard, but not verified myself is that both the LMT and KAC extractor springs are interchangeable, due to similar L1 and L2 dimensions for use.