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55 gr. BBT HP
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Author:  rsterne [ Thu Mar 07, 2019 6:03 pm ]
Post subject:  55 gr. BBT HP

I have a hot .25 cal Disco that is a genuine 100+ FPE gun, so I pulled it off the wall today to try some velocity experiments with different size bullets.... I have some 50.4 gr. FN BBTs (NOE 250-51), and also some 58.3 gr. FN (NOE 250-60), plus the HP versions as well.... I tried them as cast (0.250" nose / 0.252" drive band), and they were hard to chamber in my TJ's .25 ACP barrel.... so I sized some of each down to 0.251", 0.250" and 0.249".... I tethered the gun at 2950 psi (it is modified for 3K plus) and both bullets picked up a lot of velocity between as cast and 0.251", gained more at 0.250", and then lost about 10 fps at 0.249", presumably from a small amount of blowby….

The 58.3 gr. FN were well over 900 fps, so I thought I would tune the gun for the 55.0 gr. HP version of that bullet, sized to 0.250".... Mean looking little devil....

Image

I maxed out the preload and hit 993 fps (120 FPE), and then backed it off a turn and got 965 fps.... At that setting, off the tether, I got 2 equal shots and then a 3rd at about 940 fps, so I backed the preload out a bit more and ended up with 3 shots off tether of 956, 963 and 945 fps (111 FPE average) within a 2% ES.... Tethered, of course, it shoots 956, within a few fps.... which will give me a good platform to test these HP bullets.... The gun is loud, and not very efficient.... but at 110 FPE it should really lay a smackdown on a Marmot.... 8)

Image

This is a penetration test of the 55 gr. BBT HP in soap at 110 FPE.... The nose came apart.... penetration of the base was 95 mm (3.75")….

Bob

Author:  Daryl [ Thu Mar 07, 2019 7:01 pm ]
Post subject:  Re: 55 gr. BBT HP

For an air rifle 'pellet' rather violent cavitation and nice final expansion too.
Good looking bullet.
I think I need to do some Condor testing when the weather improves.
Bob have you tried moly coating?

Author:  rsterne [ Thu Mar 07, 2019 10:59 pm ]
Post subject:  Re: 55 gr. BBT HP

Nope, never tried it....

Bob

Author:  Daryl [ Fri Mar 08, 2019 4:39 pm ]
Post subject:  Re: 55 gr. BBT HP

I'm just about our of my MsMoly kit spray, but managed to pick up some "Lyman Super Moly Spray Lube" in a 13oz can..
I also spray all my moulds with MS Moly before using them the first time. It does not come off with casting.
It appears to be the same product as Ms Moly - in their words:
"Ideal for Coating Bullets & conditioning Barrels Excellent Mould Release Agent.
*Extends Barrel Life
*Reduces Bore Fouling
*Increases Accuracy

On the back of the can, Lyman says:
"Molybdenum Disulfide, (MoS2), is an extreme high pressure lubricant which maintains it's lubricity
at pressures above 400,000 psi - etc, etc.

I have been using moly coated bullets in my .17 CF's for going on 12 years,
for velocities up to 4,500fps.

Author:  rsterne [ Wed May 01, 2019 6:05 pm ]
Post subject:  Re: 55 gr. BBT HP

I had a chance to shoot these at 100 yards today from my .25 cal Disco with the 14" twist TJ's barrel.... Here is a 3-shot group I got while sighting in the gun.... It is actually the smallest group I have ever shot with an airgun.... and rivals the best group I got decades ago with my .222 Rem handloads.... It was shot from bags, front and rear....

Image

It gets lost under the dime.... 8) …. These were sized to 0.250", and shot at 950 fps, like the ones in the posts above.... I shot a Ground Squirrel with one and the results were NASTY.... I'll be posting a pic in the Hunting section....

Bob

Author:  Daryl [ Wed May 01, 2019 6:44 pm ]
Post subject:  Re: 55 gr. BBT HP

Very impressive, Bob & at 950fps mv. Does anyone know if this vel. is possible from an AirForce Condor?
If not, what would the gun need to achieve this?
110fpe, very impressive.

Author:  rsterne [ Wed May 01, 2019 6:49 pm ]
Post subject:  Re: 55 gr. BBT HP

Would you believe this was a modded Disco?.... :shock: …. Tethered at 3000 psi, my gun shoots 956, and off tether I only get 3 shots (135 cc reservoir), 956, 963 and 945 fps....

The Condor should be able to get there, I would think.... You need full bore-area porting throughout, and 3000 psi....

Bob

Author:  Daryl [ Thu May 02, 2019 12:55 pm ]
Post subject:  Re: 55 gr. BBT HP

I don't understand the porting, but will crank it up at some point and chronograph it. That will give me a starting point.
Thanks.

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