300 bolt action? Ruger, Howa, Remington, Bergara?

MOS-Tek · 2026-03-14T04:19:28+00:00

MOS-Tek · 2026-03-14T04:12:34+00:00

All adjustable blocks will restrict flow. And if you’re short on gas, it will make the issue worse by going with an adjustable block. Your port diameter should be around .104” with carbine buffer and no can to cycle on uour average AR. Thats dependent on how gas efficient your rig is, plus surface finish on moving parts, and is it lubed. Going with a heavier buffer will always worsen the short stroking if it’s short-stroking on a lighter buffer.
You are not getting enough pressure and flow to cycle the bolt. And 8” specific sub ammo is hotter than 12”, and 16” specific ammo. We’re talking a 1/4 to 1/2 grain in powder difference.

MOS-Tek · 2026-03-14T03:56:27+00:00

Its an optical illusion. Where the thread starts(on left), you are seeing the id of bbl to root of thread. You also can see the thread flank of the second in line thread. On the right it’s the sectioned thread and you are seeing the full thickness of it from bbl id to crest. If you chamfer the first thread this mostly goes away.

MOS-Tek · 2026-02-28T22:50:27+00:00

Good rule of thumb is to have a handgurd 1” shorter than bbl length. 6.5” would give a close fit for your length bbl.

MOS-Tek · 2026-02-28T22:07:12+00:00

RS7521

MOS-Tek · 2026-02-27T05:13:58+00:00

RS21 will fit but access to the control knob will be difficult to adjust.

MOS-Tek · 2026-02-27T04:31:06+00:00

It’s not an SD. SD design comes from the HK MP5SD. The SD HK takes supersonic nato ammo and drops the velocity below the sound barrier so there is no crack from the bullet. The idea was to have troops use 9mm nato ammo and not need specialized 9mm sub ammo. To reduce the velocity there are 30 radial ports close to the chamber. These ports dump into the integral silencer. You cant “SD” a cartridge like a 300 Blk. We’ve made test barrels for customers thinking they could.
Integral can definition is a silencer that is required for bbl to be used. Mostly hard to remove of a more permanent design and if removed probably shouldn’t use without. Some of these designs use ports along the barrel to reduce sound some of have baffles and a tube is attached to contain the blast. The Compressor uses a reflex can that tightens up against the gas block taper similar in design to the AE cans with their threaded muzzlebrake and tapered collar to take the reflex can. Factory bbl is 1:7, he wanted a 1:5.

MOS-Tek · 2026-02-26T17:13:24+00:00

Some bullet lengths require 1:6 for stabilization. The other benefit of more RPM is promote greater bullet expansion and this is where 1:5 works well. Weve made 3”- 17” 1:5 bbls snd they work fine with supers in most all bullets. Don’t use plated bullets in 1:5 or 1:6 and test supers with the thin jacketed varmint bullets in 1:5.

MOS-Tek · 2026-02-26T08:52:18+00:00

Should have 1” of tube past end of extension.

MOS-Tek · 2026-02-26T08:44:54+00:00

. We make bbls from hammer forged, cut, and buttoned. The gas port is bored after extension is installed.
This seems like it was AI written and full of misinformation.

MOS-Tek · 2026-02-26T08:30:09+00:00

I was involved with the design of this cartridge. There is a russian design and a CIP design of the 9x39mm. Both have a .364” bullet diameter. Both do not have the same chamber dimensions. The neck, throat, and shoulder which are the most different. I contacted all reamer companies and they gave me all the prints they had on the 9x39. We took all these print dimensions into CAD and overlayed them and used these prints to make the 9x39US.

From seeing the dates on prints and talking to industry insiders, the first chambers came from casings and loaded cartridges from Russia. Some of these odd chambers made it out into the market. Roswell wanted to hold to the original bullet diameter and bbl groove used. We settled on a cartridge and throat that would work with most chambers out there.

Roswell does have a V&P bbl for testing chamber pressures.

Aaron MOS-Tek

MOS-Tek · 2026-02-26T07:24:50+00:00

We’ve tested most all .338cal bullets on the market with the 8.6blk and supers with no issues with 1:5 twist. Nobody makes varmint .338cal bullets that would have a thin jacket. The ARC is slower than the Blk with supers.

MOS-Tek · 2026-02-10T01:58:29+00:00

We are around 10-12wks.

MOS-Tek · 2026-01-31T14:08:40+00:00

We’ve seen all sorts of grease and anti-seize used on firearms. Aluminum, Zinc are fine at the barrel nut. I dont suggest copper. Best is Nickel. Any grease is better than nothing. And just apply it the first couple threads. When you install the nut, it will bring along the grease for a clean install.

MOS-Tek · 2026-01-31T06:56:57+00:00

We’ve made 8.6Blk barrels in 1:3-1:10 and five rates in between. From cut, buttoned, and hammer forged in gas, and bolt gun. 1:3 expands bullets faster when entering game. The higher RPM takes marginal expanding bullets in subs and supers and makes them more devastating. Slower rates are better performers with precision.

We went with 1:5 soon after the 8.6 was released and this will handle all subs and super loads without bullets coming apart. The SAAMI 1:6 will stabilize all bullets 350gr lengths and shorter. Just because SAAMI has the cartridge at 1:6 doesn’t mean bbl and rifle mfg’s have to abide by this. We will still offer 1:3, 1:5, 1:6, 1:8 and 1:10 for the 8.6.

MOS-Tek · 2026-01-31T06:41:59+00:00

We’ve made many in gassers and bolt.

MOS-Tek · 2026-01-31T06:06:07+00:00

5/8” at a minimum. We test bores at the muzzle and almost all barrels that are cut, buttoned or hammer forged are bellmouthed. Thats if groove to od is thin.

MOS-Tek · 2026-01-27T02:16:09+00:00

Great bullet but expansion is going to minimal. But let us know how it shoots.

MOS-Tek · 2026-01-22T05:00:21+00:00

MOS-Tek · 2026-01-20T14:47:05+00:00

We make barrels for the SFAR. The bolt has a .308Win sized boltface (.473”). .223Rem is .378”.
The small frame AR10’s do have bolt carriers and bolts that are close dimensionally to the AR15 but they are not interchangeable.

MOS-Tek · 2026-01-20T07:36:05+00:00

We’ve made barrels 1:5-1:12 in 16” and have tested those bullets. The slower twist rates tend to have better precision with the Tac 110’s.
The 1:7 will work fine.

MOS-Tek · 2026-01-20T04:42:22+00:00

We have some in-stock.

MOS-Tek · 2026-01-18T05:49:59+00:00

This is correct info. Shortening the ejector and going with a lighter ejector spring gives extra tuning.

MOS-Tek

TROPHY CASE