Well, after eight months waiting on a barrel from McGowan, the Gremlin I have been wanting to build is finally a reality. I put the upper together last Thursday night, and after a few days of hand-wringing over scope and loads, I took it to the range today. Not altogether good, but a decent start. I will expand that thought below, but first, the particulars:

22" McGowan stainless barrel; 1-in-14 twist, target crown, and mid-length gas system. (Cartridge developer recommended a carbine length gas system and a 17" barrel). This is a correction based on my review of email received from McGowan barrels. Custom lower...

Loads used to check function were all cast bullets, cast with linotype and lubricated with Thompson Red Angel. Cases were new Winchester 7.62 X 39 necked up to 35 caliber and then expanded with the RCBS neck expander to accommodate the slightly larger cast bullet. Dies are Hornady New Dimension...

RCBS 35-200 FN and 21.0 grains of WC 820, seated to just below the driving band: 2.115"

Hensley and Gibbs #8 (250-grain RN) and 16.0 grains of WC 820 ,seated to just below the driving band: 2.200".

I started low in the load range because of uncertainty with a brand new wildcat, and I had FTEs on every round. I don't know if this is because the powder charge was low and lowered even more by fire-forming the case to the Gremlin configuration or what, but it should be mentioned that when the upper was first assembled the bolt and barrel lugs were so tight the bolt was sticking. It took about 80 cycles to loosen it up to where it would open with normal pressure on the charging handle. The rifle did appear to loosen somewhat, as the rounds toward the end of the 25-round test tried to eject: the bolt came back about 2/3 of the way prior to hanging up.

I see several possibilities for the FTEs:

1) a very tight tolerance between the bolt and the barrel extension.
2) too low a chamber pressure, and not enough gas pressure to cycle the bolt
3) just a new rifle period, and everything being tight.
4) the wrong gas system (I really hope it isn't that!).

One bright light in all this: the 250-grain RN cast shot into 1/2" at 25 yards. Not bad for five shots and a gas gun to boot.

I have to go to MD Anderson for an infusion tomorrow so it may be a few days, but stay tuned. I am going to wring out this Gremlin one way or the other...

Thanks for the update!
Hope the wrinkles get ironed out smoothly.
It is quite a beast to have a mag full of 35 rem power.
Pics?
Congrats.

quote:

Originally posted by Doubless:

22" McGowan stainless barrel; 1-in-14 twist, target crown, and mid-length gas system (at cartridge developer's recommendation).

Haven't built anything on an AR longer than 17" and all have been carbine gas. Sounds like you are in uncharted territory.

As for uncharted territory, that doesn't bother me a bit. Any wildcat cartridge development is somewhat uncharted. The only real issue here is the Gremlin on an AR.

Bryan, I have tried to discuss this with you in the past, but you are incredibly hard to get hold of... you don't have a telephone number, and emails go unanswered for a week at a time, if answered at all. It makes it very hard.

I am not trying to castigate you in public, simply stating facts. I would welcome your expertise in this venture, but I can't even get an email response...

There is a reason I sent you to McGowen for the project, I don't have the time to take it on at the present.

I answered all my outstanding emails yesterday, including your questions on the case trimmer.

PM sent...

What diameter is your gas port drilled out at? If in the .084-.093" range you still have room to play with. You could try a weaker buffer spring, but that might cause problems with stripping the next round out of the magazine.

Matt, we went with enhanced bolts with the builds because the X39 is notorious for shearing bolt lugs. When we got the rifles put together the tolerances were so close between the locking lugs on the bolt and the barrel extension lugs that the action wouldn't open. Lapping has helped, but there is still resistance when trying to open the bolt.

I received standard Grade I bolts today. I changed the one out in the Gremlin and am going to cycle it about a thousand times, then go back to the range. I really believe this is part of the problem, but maybe not all of it.

I am also aware of the gas port diameter issue. The Gremlin case has about twice the surface area as the 5.56 case, and it appears the port was drilled with the "one size fits all" thought in mind. I am thinking the greater surface area of the Gremlin case is causing excessive friction and with the tight bolt, it is just enough to keep the action from cycling.

And you are right; a weaker buffer spring may solve one problem and create another...

Thanks for the thoughts; they are appreciated.

If I might interject my 2 cents; a question or assumption on my part is the fire forming loads are at or near full working pressure? If so the next thing to do would be to either reduce the reciprocating mass ( a lighter carrier and buffer if possible) or cut one coil at a time till the rifle cycles. Opening the gasport should be a last option.

David Tubb, informative on buffer springs

FWIT I have nearly 3,000 rounds on a 20+ year old Colt 7.62 x 39 upper kit and thankfully no bolt problems as yet.

308, one of the issues with this rifle is the complete lack of information regarding the cartridge. To the best of my knowledge, there has been no official pressure testing of loads; the developer of the round has completely shied away from the AR platform; if you go to his website he shows nothing but barrels for the Savage. Adding to that, as you can see above, he basically told me to work with McGowan as he had no time to help me. So I and my buddy are kind of on our own. He did send me some very rudimentary load data, but there were no pressures given for any of the loads; velocities but no pressures.

I will state this: I have taken the cartridge to the point where looking at the primers, if I were ejecting them out of a bolt gun I would not go any higher. They are not bradded, but they are plenty flat. The fire-formed brass comes out looking exactly as I would wish it to, so I know I am getting full blow-out, if that is a proper term.

Information regarding this round on the AR platform is very piecemeal. I have gone to several different websites and read what I can. I do remember at one point reading where the cartridge developer talked about opening the gas port. I don't want to do that if I don't have to, but I see no use for a single shot AR, either.

Finally, although I am on disability and working with a very tight budget, the idea of cutting buffer coils is very unappealing as well. I think I will probably "spring" for a couple of lighter ones and try them if changing the bolt doesn't seem to help. (sorry for the pun...)

Did I mention that I am stubborn? I waited eight months for a barrel, and this cartridge for some reason is pretty appealing to me. I am going to work with it until something gives.

And fwiw, once the cycle/FTE issue is solved we have to figure out which mags have the best chance of working, and it looks like there will be at least some degree of modification to existing mags required. As of now there are no 358 Gremlin mags out there. The cartridge looks exactly like the 300 Whisper/300 BLK on steroids; surely something will work!

Several years back I was building a lot of custom AR's (and still am I guess) and had to reverse engineer a lot as there wasn't a whole lot of information out there. Built 17 Remington, 204 Ruger, 20 Tactical, 223's, 6X45's, 7.62X39, a LOT of 6.5 Grendals, and even a few gas operated 10mm Auto's. I did all threading, chambering, contouring, drilling gas port, etc... and figured out a lot of it on my own. Number one, as you have pointed out, is the tight bolt. How much play is there between the bolt face and the breech??? Sounds like there is not enough. Should be around .010". If that's where it's tight, just place some 220 grit on a flat surface and with good even pressure lap/sand the face of the bolt. Take your ejector out and polish that real well and put a light chamfer on it also. No reason for the bolt to be a tight fit. Take your barrel out of the upper and just fit the bolt in the extension and see if that's the hangup. Fix that, then you're going to have to open up the gas port if I'm guessing right. If the Whisper is any indication, with that bore size you're going to end up at least .100". I'd rather have the port tuned for a standard spring than to dick around with buffer weight/spring power. If you're getting partial cycle after you fix your bolt fit, try opening the gas port .003" and try it again.

Matt, after cycling the Grade II bolt about 100 times I took the rifle to the range the first time. I was doing nothing but fire forming loads, and about one out of six would try to cycle. The bolt was trying to come back, and sometimes it would come back to within about half an inch of where the brass would clear, and then hang. I am not sure why, but I have to believe it is, as you said, tolerances between the bolt and the extension.

What I don't understand is that when the barrels were cut, McGowan had the bolts for headspacing. I am wondering if they have much experience in cutting barrels for ARs.

Stay tuned, guys, and thanks for the suggestions. This is a new arena for me and I have a world of things to learn. I intend to go back to the range this afternoon to see if installing the Grade I bolt fixes anything.

If you assembled the upper yourself, take the bolt out of the carrier and install the carrier alone in the upper. See if the carrier key isn't hanging up on the gas tube. If it is, you can tweak it side to side w/ a flat tip screwdriver, and if it is too high/low bump it down with a brass punch or lever it up with an open ended wrench.

Then fix the bolt issue.

Well, at least some progress this afternoon: I had some rounds fully cycle! Funny thing is, they were fire-forming rounds: 24 grains of WC 820 behind the RCBS 35-200 FN and a CCI-200 to light the fire... the same load in a fully fire-formed case would not cycle the action, and neither would 20 grains of 820 behind a 260-grain hard cast round nose...!!

I am thinking now that the pressure band for this rifle to cycle is going to be fairly tight... it looks like now that too high is going to cause the rifle to not cycle, and if the powder charge is too low, that is going to happen as well. I did have some fire forming rounds that came out of the rifle just as cool as they could be. The ones that cycled were hot, as you would expect.

Matt, I will take a look at how the gas tube intersects the key. That may be part of the issue as well, but I do think I made a step or two in the right direction today.

Any possibility that powder burn rate could be adding to the misery? I am shooting WC 820 right now, and it is kind of fast. I have RL-7, AA 1680, and Hodgdon L'il Gun as well. Any thoughts on powders to try? I am far from an expert on "dwell time".

Probably not applicable, but h335 is good in the Grendel. I would imagine 322 or aa2200??? Just guessing there, but dwell time/pressure issues usually arise with using too slow of a powder. I would think powders that work well in the whisper with heavy bullets would be applicable here. It will be interesting how this develops. Did you get any velocities on these? Interesting round and application... I was thinking of messing with the SOCOM but component availability sucks right now.

Matt

I had forgotten about AA 2200. I have some of that as well. Will add it to the mix of possibilities, and will let you know.

the gas port for a 7.62x39 AR should be close enough to get you where you need to be.

the gas port for a 7.62x39 AR should be close enough to get you where you need to be.

335 is a great powder for the 35 remington, it should be right in the ballpark for what you need.

why did he specify a short gas system???? what was wrong with a rifle length system? the shorter the gas system, the more the problems.

Doubles, what inspired you to build the Grenlin? The spark of genesis for the cart was for a short barrel around 8-12" CQC cart for urban warfare. The longer barrel opens up a lot of powder options and range. I also saw this cart being a match for a good woods gun for hunting. It is a 300 blackout/whisper on steroids and should be quite efficient duplicating the 35 Rem. I have pondered the target capabilities of the cart for 100 yard competitions.

Boomy, it was the idea of a 35 Remington on an AR; in effect, a high capacity hog killing machine that would with any luck take easily to cast bullets and be very forgiving in the pocketbook once the initial build and function/mag issues were sorted out. There is a plethora of 35-caliber bullets in a wide range of weights, and I figured the cartridge originator would be able to help sort through anything we encountered along the way. I figured with me being a bullet caster, there really were no limits if I could keep leading to a minimum.

The idea of a longer barrel than what had been played with already just added to the attraction of doing something that hadn't been done before...

The RCBS 35-200 FN is spookily accurate at the ranges I have tried so far, and there are no issues with leading. Additionally, the 250 RN shows real promise. If I can get this thing to run and eat lead, I will have conquered it all. I am not ready to share photos, but when I have cast bullets cutting holes at 50 yards, I am encouraged.

Delloro, the only thing I can come up with is that the original inspiration for the cartridge, the 9 X 39 Grog, was, as Boom Stick noted, a short barreled weapon launching heavy bullets at subsonic velocities. It was apparently quite accurate in that profile.

We went with mid-length as kind of a guess. If this barrel doesn't work (and I think it will), we can maybe get two more barrels cut in the 22-24" length and use rifle length gas systems, assuming the cartridge developer will allow use of the proprietary reamer again. McGowan will cut the barrels, evidently, but there is a wait...

This is starting to be fun; I just hope we can work out the kinks and let you guys know how to avoid the snags my buddy and I have to fight through...

I wish you the best of luck!!

A bit of an update: 24 grains of Reloder 7 behind the Speer 35-200 FN GC bullet not only cycled the action, but was cutting holes at 100 yards yesterday evening... at least it was until the gas tube decided to move a bit and start impinging on the gas key, which kept the bolt from going full battery. That, of course, shut down the testing, as it was not immediately evident what the issue was. It appeared for all the world the bolt was frozen in the forward position, but that was not the case.

Short answer is, there is/are powder/powders that will cycle the Gremlin action and be accurate at the same time, even with a mis-matched barrel and gas system. The big challenge now is trying to find a mag that will feed the Gremlin round reliably.

The range is closed today for maintenance, but I will be back at it in the AM; I have Reloder 7 and the Speer 200 loaded up to 26 grains. I am going to take the Chrony as well and see what kind of velocities I get.

And I just found 10# of XBR 8208; may be a bit too slow, but time will tell!

This guy built a nice AR in 358 Gremlin. He might have some loads that could be of help.

http://ingunowners.com/forums/...mlin-ar-build-2.html

Boomy, I saw that thread several months ago. Looks like he is using a PRI mag in the rifle, but nothing new in the thread in over two years tells me something is awry.

Thanks for the link. Much appreciated. Back to the range in the AM with two rifles in the Gremlin chambering. Maybe the stars will align properly and something will go right!

Well, I thought I would "update the masses":

After continuing to have problems with the Gremlin not wanting to go full battery no matter which mag was used OR which projectile was loaded, I started doing a bit of investigating with a 0-1" Starret micrometer. Here is what I found:

Fired cases from the Gremlin measure .431" at the case body/neck junction.

FL re-sized cases from a set of custom Hornady dies mike .430" at the case body/neck junction.

What I am looking at is less than a thousandth of "slop" all the way around to allow a loaded round to chamber. NO WONDER THE #&%*!D cases are sticking!!!

It gets worse: I can take a fully loaded round and single load it by pushing it into the chamber, then releasing the bolt to go closed under buffer spring tension. The round will chamber, but I cannot remove it with the charging handle. Congratulate me: I have a single shot AR!!!

I have talked to Hornady, and I am told that their dies are set to .428" +/-.001" at the body/neck juncture, and they are willing to measure the dies I have. I am going to order some cerrosafe and do a chamber cast, then send the whole kit and caboodle to Hornady. They cannot help with the chamber, but they can help if the dies are out of spec.

At this point I have to wonder if a worn reamer was used to cut the two chambers, and I have a combination of too small a chamber and too large a FL sizing die from Hornady. Regardless, it is NOT a marriage made in heaven! Without chamber dimension drawings and a cartridge spec sheet, I guess I am just left to wonder.

Looks like the next (and cheapest) step in the troubleshooting process is to have Hornady cut me a custom set of dies that shrinks the body dimension another .005" or so; maybe that will insert enough clearance to let a loaded round strip from the mag and go full battery.

Sheesh... it really shouldn't be that hard!

Stay tuned; I am going to figure this out so help me Hannah!

Thanks for the update. It is the unknowns that are the biggest bother. Sorry that things are not cycling well YET. When it does you will for sure have a good sense of satisfaction. Sharing problems helps everyone learn a lot more than sharing perfect scenarios. Thanks.

Are the exterior demensions the same as the Grendel? Wonder if you could just bore out a grendel FL die for the neck diameter of the 358 and give that a go. Never had a problem with a sticky chamber on a grendel AR. For that matter send me the barrel and I'll take a turn or two with the Grendel or 264 LBC reamer and clean up the chamber to the shoulder. May be ALL you need. Want me to measure fired grendel brass out of my chambers and see where it's at?

Matt, I sent you a response via PM.

Thanks!

Replied to, and re-reading about your last issue, yes, it may be a tight chamber, but more likely it could just be too tight of headspace. Can exhibit the same problems you're experiencing. Easy fix is to face .002" off the bolt face on the lathe and 'viola' you're done. Otherwise grind the top of your shell holder down a hair and see size your case a touch more and see if it then chambers more easily.

I re-read over some of your earlier stuff too and there may not be enough clearance between the lugs and the face of the barrel. You should be able to feel a little back and forth play (.007-.010") with the bolt locked into the extension. Really sounds like they fitted it with too tight of tolerance.