Subsonic 9mm troubles in a BRP gun

[Starvingboy]

I'm having troubles with 9mm 147g ammo. It finally motivated me to stop lurking and join this forum.

ANYway, My I'm trying to load something quiet for my 9mm BRP. I test fire vertically into a bucket of sand in the basement. Not the safest perhaps, but it works for me.

147g/3.6g of TiteGroup ran away. Apparently not enough zip to send the bolt far enough to trip the sear. I bumped the load up to 3.8g, same problem. By this point, the ammo is pretty hot according to the specs I have.

It COULD be the fact that I'm firing the gun vertically, but I'd rather the angle not be a critical factor in reliability

 

[MPA guy]

I typically only load 147's at 3.3 or 3.4 gr of titegroup.

It cycles heavy slowfire open bolts, uzi, scorpion, and anything else I feed it to.

I wonder if you don't have something else going on besides ammo power.

 

[Starvingboy]

Cool, that gives me something to go on. This is my first time messing with heavy 9mm bullets, so I'm trying to be cautious.

 

[TheColtCollector]

Spring pressure on your bolt is also a factor to consider

 

[K2]

Welcome Starvingboy,

All guns have their favorite loads that make them run reliably. Depending on how well aligned/worn-in/recoil spring condition might be, some loads that work well in one gun will not cycle another gun.

I do know that many of my supressed 9's will run on 3.6gr TG with 147RNx1.15 oal. I know of many guns at our monthly matches that will not run unless fed with 3.8gr TG 147RNx1.15oal.

Note I mention the OAL of the cartridge. Heavy 9x19 are sensitive to OAL. Shorter means more pressure rather quickly. I also run 160RN in the 9X19 and it is very sensitive to OAL when it comes to pressures.

It is helpful if we know the bullet being used and OAL of the loaded cartridge. For instance, if your 147 is a HP and set at 1.16 OAL, the pressure is much lower than a 147RN set to 1.14 OAL.

Good luck with your loads. If your primers are missing after firing the round, the pressure is likely excessive

K2

 

[MPA guy]

I normally run mine 1.100" @ 3.3 gr TG.

YMMV, FWIW, etc.

 

[Starvingboy]

Thanks for the input guys, I'll keep tweaking. I figured "More Powder" was not the answer, and I was running my OAL at the max length. I was hoping someone had a BRP/Stemple set-up to compare against, but they are apparently not that common (?)

 

[r]

You may want to latch onto an extra recoil spring and start slowly clipping it down a 1/4 coil at a time

 

[Scossum]

I would highly recommend calling or emailing Brian Poling at BRP Corp. That's one of the best things about these guns is that you can always count on Brian for technical support after the sale. He's a very knowledgeable and willing to help!

 

[chili17]

Try COAL of 1.135-1.145 with 3.5gr of TG

 

[nklf]

Which recoil spring/buffer are you running? If you look at your owner's manual for the BRP, there are different configurations for full power vs. reduced loads. I have not tried to run subs in mine yet so I can't advise which combination will work best, but look at the manual and call Brian. He is very helpful and willing to walk you through the proper set up for your ammo.

 

[strobro32]

I'm using 147 Extreme plated, 3.6 TG with 1.14 coal
I use the RF-1 configuration on the BRP STG U9 SF .

EDIT: I had to correct this as it ran away with me this morning too. I'm going to try the RF-0 configuration or the reduced spring too.

 

[Starvingboy]

I'm using 147 Extreme plated, 3.6 TG with 1.40 coal
I use the RF-1 configuration on the BRP STG U9 SF .

That's what I was looking for. I'm running a U45 set up in the 9mm configuration, lightest bolt, standard spring, near as I can tell. So I need either the dedicated 9mm set-up (Been looking for an excuse to buy a Suomi conversion) or trying for a lighter recoil spring. I'll sling an email off to Brian. Every time I call, it ends up burning up an hour or so just BS'ing about guns. I can do that at the creek next month and not get funny looks at the office.

 

[nayo]

3.9g of titegroup get me 930fps on the chrono!! you need more powder to push that bolt back

 

[chipster]

I'd be a bit careful, with the Hornady 147gr FMJBT at 3.6gr of TG and 1.160 OAL I was starting to get pressure signs on the primer/head of the case. I toned the OAL back to work better in lined(glock) mags and was seeing the same thing at 3.5gr of titegroup at 1.145 OAL. If you are running 3.8+ and still not cycling I'd have the gun checked out.

FWIW - if you are loading XTREME bullets, the 165gr is an amazing bullet. I read that folks have that running in most things with 3.0grs of titegroup. I scrapped that due to same pressure signs, but have worked up a load with Longshot. Running a mag primer I'll load 3.6grs of longshot at a <1.169 OAL for the MP5K/Colt 9mm subsonics. I'll run between 3.8 to 4.0 to run my UZI, but that is top end.

 

[Starvingboy]

Just reporting back in: Brian at BRP hooked me up with the light-weight spring, and it ran perfectly under my test conditions, (Vertical, sand bucket) using 3.6g titegroup/147g plated. Also, when I popped up from the basement to ask how loud the report was, the reply: "How loud was what?"

 

[strobro32]

Just reporting back in: Brian at BRP hooked me up with the light-weight spring, and it ran perfectly under my test conditions, (Vertical, sand bucket) using 3.6g titegroup/147g plated. Also, when I popped up from the basement to ask how loud the report was, the reply: "How loud was what?"

I had the same problem today too. Are you using the reduced main spring+ buffer+ aluminum bolt extension or the buffer +reduced mainspring+ aluminum bolt extension?

 

[strobro32]

So I tested the new 147 gr, 1.14 COAL, 3.6-7 Titegroup combo with the BRP STG U9 today.

Backwards buffer + reduced power mainspring + aluminum bolt guide. This seemed to work best.



I also had a OOBD with the new suppressor on one of the last shots. I was not wearing hearing protection because I was listening to the performance of the modified suppressor.

My ears still hurt.... A LOT. The OOBD toasted the extractor spring.

 

[Starvingboy]

Backwards buffer? That's a new one on me. I ran 5-6 hundred of my 147's through my gun, with no issues*.

*(well, Ok, ONE round just sort of sat in the chamber. Didn't fire, didn't extract, but popped out with the use of my fingernail. I forgot to save the round for analysis)