SUB-SONIC Grendel loads

[txgunner00]

Picked up some Unique today. While at the local reloading store I got into a conversation with the manager and he put me in contact with a local class 3 dealer that shoots a lot of suppressed sub-sonic. Unique is also one of his favorite SS powders and he stated he uses Kapok (natural fiber pillow stuffing) for filler. Hopefully I can get to the range this weekend.

[zeeb_m4]

Any updates on the progress of the load???

[txgunner00]

Just got back from the loading bench and collected some data.

I checked my fire formed IMI & Winchester brass looking for the one with the least amount of capacity and was surprised to find they were nearly identical. Both held the same amount of Unique (18gr +-) and their average weights were nearly the same (130gr +- vs. 115+- gr for AA brass). I was told by Mr. Alexander that IMI brass was much thicker than anything else but it seems Winchester is just as thick. I selected the Win brass because I've read it is relatively soft which seems true (checked by "bite testing").

The cases held an average of 12.5 gr when filled to the level where the bullet seated at 2.220" would just touch the powder. This gives me a load density of approximately 50% using a starting load of 6.5 gr.

Now I just need to go shoot them.

[warped]

I would not doubt that the difference in the quality of the brass can result in a slight weight difference.

Not all brass is equal in composition. sometimes the zinc levels are different etc.

[Rapier]

I got out Saturday with my 16 inch, no can attached and 140gr Hornady Interloc bullets. I decided my 1-9 twist would not stabilize the 160s as my only other 6.5 barrel in 1-9 will not stabilize a 140 Barnes copper solid, which is longer than a 140 lead core. If you get a 160 to make round holes in a 1-9 twist let me know, if you would. Anyway here is the data from my run:
All Unique / 97 degrees
6.5 gr w toilet paper 749 fps at 10 ft round holes, action opened about 25% but no function
6.5 gr w/o toilet paper 723 fps
6.2 gr w/o toilet paper 713 fps

All loads put bullets down range and were about 11 inches low, POA to POI at 100 yards. Barrel was broken in with Sweet Shooter which contains Tecrolan and coats the bore, filling the metal's pores, making the bore slick. I use the process on all of my match guns.

So I will need to jack up the load to get to 1,100 fps, which I did last night at 7, 7.5 and 8gr. Now I will drop back to testing at 50 yards as this is a night hog over a pond deal.
Ed

[bwaites]

I think the only way a Grendel is going to cycle is with a very heavy (think 200 grains) bullet and the right powder. I just have no idea what that powder is going to be, and the bullet will probably have to have a tungsten core to be that heavy and fit the case. That said, with such little powder volumes, it could sit way down in the case!

[txgunner00]

I finally was able to get out and shoot the test loads I made a month ago.

7.4 gr of unique behind a 160 gr. hornady interlock averaged right at 990 fps. All round holes and grouped at about 3" at 100. POI was 20" below POA.

Barrel- 20" Satern
Case- fireformed Winchester
Primer- Federal Gold Medal Magnum Match
Temp was 98-99 deg.

[Rapier]

Tx,
Did you get the cases to eject or like me, the bolt unlocked and slid back a touch, only to go back forward into battery?

Sounds like you could go up another 2 tenths or so to get to 1,000 fps if 1,000 will work for you. Did you calculate your super sonic speed for your location. You can find the formula on line for altitude. I am at 245 feet. Speed of sound at sea level = 1116.13 feet per second

Are you running a 1-8 twist?
Ed

[txgunner00]

These loads only pop the bolt back a bit then it locks back in battery. I'm not really after a load that will cycle as I built my grendel on a side charging upper. I run it like a bolt gun.

I may try to push them a bit more but I have not calculated the speed yet. I'm at 1000-1200 depending where I'm hunting.

1-8.75

[Wally Bear]

What about lightening up the bolt, buffer and buffer spring to allow the gun to cycle? Could you set your gun for one load or another? I brought up an idea on another forum about drilling and tapping a couple of holes on the bottom side of the bolt carrier at the back in order to insert weight inside the back of the bolt to adjust the weight to regulate the firing rate and to tweak the felt recoil.

[mtn_shooter]

If I recall, the trick is not to use fast burning pistol powder, but to use slow burning magnum powder. It's inefficient in the chamber, producing low velocities, but it's slow burn time means there is enough pressure at the gas port to cycle the action.

[txgunner00]

If I recall, the trick is not to use fast burning pistol powder, but to use slow burning magnum powder. It's inefficient in the chamber, producing low velocities, but it's slow burn time means there is enough pressure at the gas port to cycle the action.

Interested- any clue where to look for more info on this? I have many, many LBS of 50 cal powder...

[mtn_shooter]

Interested- any clue where to look for more info on this? I have many, many LBS of 50 cal powder...

No I don't have any info, sorry. I just remember that there was one member who used slow powder on the old forum and had a cycling subsonic load with standard springs/buffer/gas system etc.. Next time I make it home I want to try it with US869.

[txgunner00]

I have that powder as well as H50bmg, IMR5010 & Accurate 8700. US869 or 8700 probably would be better choices because the are ball powders.


I don't suppose you could overcharge with a slower powder. Do you think stating at 75% load density and working down is a good plan?

[mtn_shooter]

Yes. I was going to do roughly that. If the charges got too light, pack it with a filler to keep from detonating.