Vent Liner Shape
 

I have wanted to do this test for quite some time now. The dome shaped vent liner sold by Lehigh has a 0.032" flash hole. It seemed the flat head vent liner should also have a 0.032" flash hole for a fair test, so one of them home made vent liner had to be used for a hundred or so shots before it also had a 0.032" flash hole. The home made vent liner start out with a 0.028" flash hole, so had to be shot to grow the flash hole to 0.032".











The V2 Accura was used for this test because the QRBP is so easy to remove, and replace. The test was done by installing the Lehigh vent liner in the QRBP, installing the QRBP in the rifle, and then loading the rifle with 270g Deep Curl, 100g BH209, smooth green Harvester sabot, and STS primer. The clock was located at 11 yard, and the target was about 100 yard out.

The load was fired, then the vent liner was changed to the flat head liner, and the rifle loaded, and fired. Then the vent liner was changed to the Lehigh liner, and the rifle loaded, and fired, then the vent liner was changed to the flat vent liner.......................... This was done for 10 shots each alternated vent liner. Shooting was steady until the wind blew the target stand down. Shooting stopped whilst i walked out to 100 yard, stood the target up, and walked back. Then shooting was steady until the wind blew the clock down. Shooting stopped whilst the clock was stood up. The barrel wasn't intentionally allowed to cool, but it never did get what i would call hot. Temperature was about 40 degrees at the start, and increased to about 50 degrees, and strong winds. The domed Lehigh liner was used to punch the top target.










.......1817 fps............ average of last 8 shot..........1813 fps






???

Neat test Ron. Looks like a draw to me.

Semi

The advantage of the Lehigh design really has nothing to do with velocity. It is the amount (efficiency) of heat and gas it can deliever/transfer to the the load (by design) and the reduction of blowback pressure on the nose of the primer (also by design).

It seems to me that efficiency of heat and gas go hand in hand with velocity. Wouldn't more efficiency lead to higher velocity? The data show both vents result in the same velocity--hence both vents are equally efficient. This is what the data show. How can one argue against the data? The data indicates both vent design are equally efficient does it not?








The primer on the left were ignited when the domed vent was in place. There is no visible evidence that they saw less pressure than the primer on the right; is there?? Where is the scientific evidence that the domed vent reduces blow back pressure? Where is the evidence? What data shows that the domed vent results in less blow back pressure? To my knowledge--none.



It seems to me that scientific conclusions should be based on data, on data alone.

ronlaughlin

I believe you are may be partially incorrect in both of your assumptions.

Please look at this target shot to check velocity changes with different primers. There primers all produce different burning temps and volumes of gas. Compare the velocity difference between them. One thing that helps this test, as Lee has already told you on another forum, is the shape of channel in the Lehigh Vent Liner which allows better efficiency for all primers.



If you look carefully you will see the weakest primer of them all a Remington 209-4 (a 410 shotgun primer) actually produced the best velocity. It does not produce as much gas volume as the other primers and it is able to transfer through the vent liner because of that. Bottom line is it still ignites BH just fine and with a very slight increase in velocity.

I do not have the abilty to explain to you why the dome shape helps reduce the blow back pressure through the Ventliner and BP to the nose of the primer. I have tried before and have failed at a very simple principle of 'angle of incidence = the angle of reflection'. Gas pushing back on the nose of the Lehigh vent liner is deflected on an angle that will not allow all or most of it to go back through the vent liner. From there you are on your own and you can decide yourself if it of any use to you. Others believe it is.

The data i collected was done alternating the vents. That data showed no significant difference between them vents. Your data was collected using one vent, one vent. How is it relevant? How is data collected using one vent relevant to comparing different vent shapes?

Also, the validity of your conclusion is questionable. Somehow you are able to conclude that the domed vent is better, because the last shots from a warm rifle/breech plug, are a higher velocity. To me that seems to be a non sequitur. It is only natural the last shots over the clock from a warm barrel/breech plug will be faster. This shows up in my data too.

Perhaps the reason you don't have the ability to explain why the dome shape reduces back pressure, is because it doesn't.

This statement is 100% wrong Ron.

I tested both ventliners in the Savage. The Savage is buy far the most pressure sensitive on primers then any other ML made. And this incudes CVA. The flat ventliner bulged more primers buy far from the dome ventlinter. Even the domed ventliner in the savage would bulge some as well. The domed ventliner made the over all pressure on the primer substantially less/better.

The above testing was done with smokeless powders. Results could change with BP substitutes but i doubt it.

Ron,great work and testing.i agree visual conclusions are far stronger than words.in this case the old cliche (pictures are worth a thousand words applies) keep the good work up.

Pressure/Smessure. There may be a difference, but the only way to know for sure would be with a strain gage. Ron's side-by-side test shows no difference in three observable factors - group size, velocity and primer fouling. So as far as I'm concerned there is no practical difference in the two.

Exactly, thats why he's wrong. You guys are funny :biggrin:

Good testing Ron. It is good to see these tests done by an unbiased source. Thanks for doing it.

Grouse, let's assume there is a pressure difference. But if the group size is the same, velocity is the same, and breech cleanliness is the same - who cares? One is as good as the other.

The assumption is with that particular load and primer you are correct. But as you progress up the powder scale and projectile weight especially with BH the pressure becomes more significant, especially if you are not using a primer that has 0 head space. My point and only point about pressure on the nose of the primer is the dome design does reduce this pressure to some extent, as also does the volume capacity of the flash channel.

Also as an added point not all guns on the market have or are set for zero head space - then the blow back pressure becomes even more significant - not necessarily because of safety but cleanliness of the breech area.

Even in a closed breech the difference can been seen if you are not using the same length primer from shot to shot - again effecting only cleanliness not safety.

A lot of people seem to prefer the Remington STS which is a shorter primer and unless you set your rifle to 0 headspace for each individual brand of primer cleanliness will be effected. Do all people have the ability to set 0 head space for the primer of their choice?

To my knowledge, in all of the forums, and blogs, on all of the internet, and all of the world wide web, there is no empirical data to support that statement.

As long as the primers are not sticking you are exactly right. Different primers have different results. But either way, both ventliners work. I dont know who said they didnt.