Breech Plug Comparison

[ronlaughlin]

Today we went to the hills to compare two breech plug. Bullet velocity from each plug was measured. One plug is sized for a vent liner with a 3/8" head, and has a 5/32" flame channel. The other is sized to receive a vent liner with a 5/16" head, and has a 1/8" flame channel. Both vent liner have a 0.028" flash hole.













The clock ended up about 14 yard out. Rifle used was the V2; load was 270g Deep Curl, 110g BH209, green Harvester sabot, and STS primer. Powder was dispensed into tubes by Redding 3-BR measure.

[lemoyne]

That is very interesting. While some would look at the total velocity what impresses me is the difference between high and low.
5/32 shows only 11 feet difference while the 1/8 shows 27 feet per second difference
,the 19 feet per second faster by the 1/8 is almost immaterial by comparison to the consistency of the 5/32.
I have a question: with the velocity starting high and tapering down, were both groups started on a clean barrel?

[Breechplug]

Not too much gain from one to the other, more importantly how were the groups from each BP? And Im surprised that the FPS's wer'nt more close, they seemed to jump a-lot.
(BP)

[ronlaughlin]

lemoyne


The first shot using the plug with the 1/8" flame channel was on a cold clean barrel. Then the third, fifth, seventh and ninth shot. The shots by the plug with the 5/32" flame channel were the sixteenth, seventeenth, eighteenth, nineteenth, and twentieth shots through the barrel.

[ronlaughlin]

Originally Posted by Breechplug

.......................how were the groups from each BP?...............(BP)

Will get a picture of the targets, and post it later.

[onetohunt]

Originally Posted by Breechplug

Not too much gain from one to the other, more importantly how were the groups from each BP? And Im surprised that the FPS's wer'nt more close, they seemed to jump a-lot.
(BP)

That's exactly what I was wondering also.

[ronlaughlin]

Range was about 100 yard.

To me the only shot that seemed to jump far out of the set was the first though the plug with the 1/8" flame channel. That was the first shot from a cold clean barrel. To me, all other shots were just fine, and seemed quite consistent. These loads were all measured by volume, using a Redding 3-BR measure, and dropped into tubes which were carried to the hills, and poured into the rifle barrel.

Bottom target was shot last using the breech plug with a 5/32" flash channel. These were the sixteenth through twentieth shots through the rifle. Chances are good, i was kinda bored by then, and did not do my part. The middle target was shot with the breech plug with the 1/8" flame channel. The ventliner was switched between shots, but the same plug was used. Half the shots were when there was a 0.028" flash hole; the other half with a 0.034" flash hole.

The top target was shot using the breech plug with a 5/32" flame channel, without the vent liner in place. Essentially, the flash hole was 5/32"; velocities were inconsistent, and primers had to be pulled out using a pliers. These primer exhibited sign of excess pressure.

Further testing will be done.

[ronlaughlin]

Originally Posted by lemoyne

................................
5/32 shows only 11 feet difference while the 1/8 shows 27 feet per second difference..............................

That isn't correct.

The 5/32" flame channel had a 27 fps total spread.

If one tosses the 1929 fps shot on a cold clean barrel, the 1/8" flame channel had a 16 fps total spread.

The 1/8" flame channel had the least spread when comparing fouled barrel, and it also had the highest velocity.



More testing is required.