Who doesn’t like a great deal? But is it worth it? Let’s take a look and find out.
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TL;DR: It ran fine in Colt and Glock setups, but I’ve been alerted to the fact that it MAY have an interference issue in some Glock magazine setups, depending on magazine height in the lower. May 2044 update – they fixed it! See update at page bottom.
The Mercury Precision 9mm bolt is offered by Davidson Defense, which seems to be part of a suite of websites which includes davidsondefense.com, deltateamtactical.com, omegamanufacturinginc.com, and mmcarmory.com. These sites offer very low cost accessories and parts. I’ve noticed that they seem to have a reputation for offering some products with questionable quality.
As part of their Fall Sale, I saw that the Davidson Defense site was offering the Mercury Precision 9mm bolt for $54. This was a price that was too good to pass up. The bolt may alternately be listed as the “United Defense Labs” 9mm bolt (not to be confused wth “United Defense” without the “Labs” added to the end.)
This bolt appears to have the same profile as many bolts that I use and recommend, including those from Kaw Valley Precision, B.Kings Firearms, Brownells (hybrid), and many other companies. However, the Mercury Precision bolt is a little different.
I received the bolt in a foam sleeve and it appears to be well machined and has a consistent coating (listed as Nitride).
The bolt weighs 13.6oz., which is lighter than my other similar bolts (14.7oz.), and very light for 9mm. A good buffer to use with this bolt would be the KAK Industries 8.4oz. “gold top” extended-length deadblow buffer, or something heavier.
The rear weight is removable for use with a Law Tactical folder mechanism. Otherwise, the bolt weight should be left alone.
The extractor is not a mil-spec extractor, but it’s very beefy.
Extractor tension is critical for proper ejection. A typical AR-15 (and most 9mm) extractors have a “4-coil” spring, a rubber post inside the spring, and an O-ring around the spring to increase extractor tension. This extractor only had the 4-coil spring, but it had no problems with ejection. Testing by myself and several other people has shown that adding the post and O-ring can actually cause this type of extractor to fail, so it seems best to leave it as-is.
The extractor is held in with small roll pin. When removing the extractor, some little metal machining chips fell out (at bottom of picture below). This doesn’t indicate a problem with the bolt. It just means that the shop worker didn’t clean things up during assembly. I think it’s a good idea to completely disassemble any new part before use, if possible, and give it a good cleaning just to keep things like this from causing any future problems.
The firing pin has some sort of coating on it, and is held in with the typical split “cotter-pin” type pin. The firing pin spring has 9 active coils and required about 28oz. of pressure to compress to full firing pin protrusion from the bolt face. This seems to be a pretty typical strength for a 9mm firing pin spring.
I took it out to the range and ran a little over 100 rounds through it…
I had no malfunctions and ejection was very good.
I’ll keep running rounds though it and see how it goes. I have seen some positive reports about this bolt, including one person who owns several and says they haven’t given him any problems.
UPDATE: WARNING FOR DEDICATED GLOCK LOWERS (Fixed – see update below)
It was just pointed out to me that the contour of the bottom of the bolt MAY hit the right feed lip of a Glock magazine. I didn’t notice this with my Spikes Glock lower, but upon closer examination it just *barely* touches. If I push up on the magazine, it becomes a problem and can interfere with bolt travel. Take it for what you will – I can only test with what I have and it ran fine at the range. For other Glock lowers it could be a gamble – it may work fine, it may not.
UPDATE 2: Regarding the ejector
This ejector design only uses a 4-coil spring for tension, without the typical rubber post and O-ring found in a standard AR-15 ejector. Another owner tried adding the “missing” post and O-ring. They report that bolt continued to extract and eject properly with the post added, but failed to eject properly when the O-ring was also added. I experimented with my bolt and got similar results. This ejector design simply does not require either one and should be left as-is.
Update 3: May 2024 they fixed the ridge on the bottom!
A Reddit user posted pictures showing that the new Mercury Precision bolts now have the 90° ledge trimmed way back so that it doesn’t catch on Glock mags. Hooray!
Blowback9.com 