OAL/ Pressure

[Bullet]

Jam length test.

Well I’m back from the range. Here are the results I have.

I’m shooting 308 in a Shilen barrel 1/12 twist. I am shooting Burger Moly 185gr VLDs. I used Lapua brass that has been fire formed. The two cartridges were identical except one was seated into the lands and the other was seated off the lands.

The Jam length for my rifle measured 3.300. The cartridge that had the bullet seated into the lands measured 3.297. The cartridge that had the bullet seated off the lands measured 3.276. The distance to the start of the lands measured 3.277. All measurements were made using a Sinclair bullet comparator.

One cartridge had the bullet seated into the lands .020. I loaded 3 of these cartridges.
One cartridge had the bullet seated off the lands .010. I loaded 3 of these cartridges.
All were shot through my chronograph and velocities are listed in fps.
N550 powder 44.0gr was used for all loads.

Bullet seated into the lands .020 –
Average - 2488
High – 2500
Low – 2480
ES – 20.1
SD – 10.5
AD – 7.9

Bullet seated off the lands .010 –
Average - 2508
High – 2517
Low – 2501
ES – 15.7
SD – 8.0
AD – 5.8

The cartridge seated into the lands had less velocity than the one seated off the lands. I believe this is because the longer cartridge in effect has a larger combustion chamber, which will lower pressure.


Maybe this will put an end to another myth.

 

[Dave P]

A couple of variables that are hard to pinpoint: smaller case capacity (shorter OAL) will raise pressure, like you saw via the velocity. Hard seating the bullets into the lands will increase the starting pressure, to get the bullet moving, but also result in a larger case volume (lower pressure).

Those are very nice SD's in any case! How was accuracy?

Dave

 

[Ol` Joe]

Maybe this will put an end to another myth

I have to disagree with your conclusion. The sample is too small to have much meaning, a 20 rd string with both loadings likely will show the velocity spread to overlap and both averages you show falling in the ES. The other problem I have is you`re measuring velocity, not pressure. You can`t say for sure the pressure is lower simply because the velocity is. I don`t even know for sure the small case capasity change can offer a measureable amount of difference.

Here are a few loads I recorded useing a pressure Trace unit and Pact crono with a 6.5x284 and 270 Win. The psi figures a not calibrated but do represent the pressures changes very closely. Factory ammo max pressure in the 270 was 55+K and a 5K loss in pressure from 60K in a lab test bed to a hunting rifle is a reasonable expectation. The figures are the averages of 5 rds and all are fired on the same days from the same components loaded on the same tooling at the same time. The loads vary in 0.5 gr powder charge increments only.

270 Win - 140 gr Hornady SST- R22 - WLR primer - Win case

53.5gr = 2935 fps & 48386 psi
54.0gr = 2885 fps & 45633 psi
54.5gr = 2991 fps & 52123 psi
55.0gr = 3035 fps & 50550 psi

6.5x284 - 129 Hornady SST- H4831sc - WLR - Lapua case

49.0gr = 2820 fps & 46909 psi
49.5gr + 2809 fps & 47557 psi

As you can see pressure and velocity are closely related but do not always seem to be linear.
I think I`ll have to try a few rds with the changes you tried and see what I find from them. I see this question often and am starting to wonder myself. The test will have to be of more then one load in more then one rifle though and I don`t know how broadly true the result will be from the small amount of testing I can do. It will be interesting though and if I find time to do it I`ll post the result.

 

[Bullet]

Dave P

I only shot 3 shot groups and didn’t measure all of them (I tried 6 loads) only the best 1 ¼ at 200 yards. All of my loads today were to slow but I started the powder low because I wanted to see the difference in velocity between in the lands verses off the lands.

Ol` Joe

Maybe this will put an end to another myth.
When I said this I was referring to the myth that loading into the lands will increase pressure to dangerous levels. I believe that if pressure had increased enough to be dangerous there would be a big velocity change when seated into the lands (which did not happen). If you test this more thoroughly I be interested in your results. By the way I believe that a lot of benchrest shooters and target shooters have been loading into the lands for some time with no problem. I believe that the general shooter (myself included until lately) is behind in the present knowledge (believes the myth) and this is why I posted this. This is not for every rifle and maybe not for every reloader either, but if your rifles up to it and so are you, you just might find that loading into the lands will possibly get you the most accuracy. One thing for sure if you never seat into the lands you will never know.

 

[USSR]

Bullet,

I have to agree with Ol' Joe, nothing here to draw any conclusions on. You seem to be drawing a conclusion from low charge/low pressure loads, and assuming that you will get the same results with full charge/high pressure loads. Pressure does not increase in a linear manner with increasing amounts of powder, so I think you will find that once you get up in the normal pressure range you may get different results. If you want to make the claim that seating into the lands doesn't increase pressure, you better test at higher velocity/pressure, and use both fast and slow powders. Just MHO.

Don

 

[Bullet]

USSR Quote – “If you want to make the claim that seating into the lands doesn't increase pressure.”

This is what I said – “Maybe this will put an end to another myth.
When I said this I was referring to the myth that loading into the lands will increase pressure to dangerous levels.”

Ol` Joe are you the same Ol` Joe that posted here –

http://www.thehighroad.org/showthread.php?t=166871

All I did was try the claim made in the above thread. My findings seem to be the same as suggested. I’m no expert and I don’t have a lab to test this but I believe this is right if you don’t where is your proof. I've heard that seating into the lands will cause DANGEROUS pressures and nobody seems to question this. Why do people assume this is true with no proof, but if someone states the opposite proof is always required?

 

[Ol` Joe]

Bullet, Yep, I`m the same "Ol` Joe".

I`m sorry if I misunderstood your line of thought. I was under the impression you were trying to say a rise in velocity with the bullet seated deeper was an indication the pressures were also higher, and the lower vel of the load in the lands was indicating the pressure wasn`t effected or was lower. Neither is always true, and the pressure changes need to be measured not velocity to make this claim valid. I was simply trying to show the amount of change in velocity doesn`t always mean similar pressure variations.

I've heard that seating into the lands will cause DANGEROUS pressures and nobody seems to question this. Why do people assume this is true with no proof, but if someone states the opposite proof is always required?

People whom "ASSume" have already made their mind up, right or wrong it`s already been "proven true" in their mind. The idea of something challanging their beliefs has to include "proof" if it`s a valid idea. Human nature I guess, and I likely am as guilty as anyone else...

 

[Bullet]

Ol` Joe

I’m no expert and you seem very knowledgeable. Thank you for your replies.

“People whom "ASSume" have already made their mind up, right or wrong it`s already been "proven true" in their mind. The idea of something challanging their beliefs has to include "proof" if it`s a valid idea. Human nature I guess, and I likely am as guilty as anyone else...”

I believe you are right and I probably do this too.

 

[Bullet]

Ol` Joe

I really like your signature.

Why shouldn`t truth be stranger than fiction?
Fiction after all, has to make sense....Samual Clemens

 

[redneck2]

I think you're making a perhaps dangerous assumption here....that seating into the lands doesn't cause dangerous pressures. Maybe not in this application, but the more I read about handloading, the more I find I don't know, except one thing....never say always and never say never

There was an article somewhere that showed that just changing brands of primers in rifle rounds could change pressures something like 6,000 psi. Now, think about all the variations in just one rifle round. Bullet weight and brand, powder amount and brand, case brand, primer, seating depth, temperature, chamber dimensions. Hard to find absolutes with that many variables

Weatherby says that loading their rounds out to the lands will create extreme pressures.

While experiments like this may be interesting, they prove little if you don't have enough for a statistically significant number and no method of measurement

I've thought about getting one of the portable labs that measures chamber pressure. May be interesting.

 

[Bullet]

Rounds loaded long enough to "jam" into the lands are loaded and shot every day by Benchers and other ultra accuracy shooters and ordinary folks that have found or feel that seating a bullet INTO the lands gives them more consistent results. This is usually done working from the bullet position backward. That is to say, the cartridge length is determined and then the load is worked up. As thousands of shooters do this, one has to assume that it is safe using the proper reloading techniques.

When changing any component of your cartridge you should watch for pressure increases. You might want to consider changing seating depth as another component and watch for pressure changes the same as with any other component.

From above –
This is not for every rifle and maybe not for every reloader either, but if your rifles up to it and so are you, you just might find that loading into the lands will possibly get you the most accuracy.

Some people get it others ….. should leave it alone.

 

[Khornet]

In my 03A3

with a 1943 2-groove GI barrel, I found that touching the lands didn't give as good a result as .005 to .010 off the lands did. YMMV.

These were fully-prepped cases: sorted by weight, pocket uniformed, flash hole reamed, neck turned, and sized with a Wilson bushing-type hand die, using 4064/50 grs and a CCI large rifle primer with a Hornady 150 gr spitzer flat base hunting bullet. Length was measured with a Sinclair comparator, and depth to touch lands established with a Sinclair gauge.