Is too much OAL dangerous?

Mosin-Marauder · January 28, 2016, 10:21 PM

I was loading some 7.62x54R in my Mosin with 51.2 grains of H4350 and a 174 Grain SMK, and I was wondering, if I seated them too long could it harm my rifle or me? I seated them pretty long and when I tried to chamber them it chambered fine, and I got rifling marks from just below the Ogive down to about a 16th of an inch above the middle of the case. I think it may like shooting off of the lands, I've since seated them a bit shorter (maybe a sixteenth more into the case) would this be dangerous for my rifle or me? Just thinking about pressures and stuff I just thought I would be better to ask than to not. Thanks for your help!

reynolds357 · January 28, 2016, 10:45 PM

It would not be dangerous unless your load was already bordering on being overpressure. Eliminating the "jump" to the rifling raises pressure slightly.

Tsquared · January 28, 2016, 11:14 PM

You don't want to have your bullets touching the lands of the rifling. Keeping the bullet off the lands as it has an affect on accuracy and an important affect on safety in regards to pressure. You need a little jump there.

Mosin-Marauder · January 28, 2016, 11:27 PM

Roger that, I'll back down the bullet until it is barely off the lands.

T. O'Heir · January 29, 2016, 02:22 PM

Bullet would get pushed into the case or gets stuck in the rifling and stops going into the chamber. What usually happens is the bullet gets pulled out and powder goes everywhere upon opening the action.
Your rifling marks indicate your OAL is too long though.
Max OAL with the bullet is 3.037".
The off the lands stuff is a load tweaking technique that you can do after finding the load. Very much doubt it'll make any difference with a milsurp Mosin-Nagant.

**Unclenick** · January 29, 2016, 05:10 PM

Mosin-Marauder,

Allow me to correct some of the above. Many bullets shoot best seated into the lands. Benchrest shooters did this routinely for years. When I went to Mid Tompkins Long Range Firing School, he explained that he and his whole family of world champion long range shooters use "soft seating", where in the neck tension is minimal and the bullet is seated out too far on purpose and finishes seating using the throat as the seating dies when they chamber the round. Berger recommended seating its VLD bullets 0.010" jammed into the lands for years.

The reason people fear seating into the lands, other than the problem of pulling bullets that T'Ohier mentioned (and that is a problem Tompkins mentioned; you have to be at a range that allows you to point the muzzle up while unloading if you are going to use this method), is that it raises pressure if you don't adjust the powder charge to compensate. But if you develop the load from the start with the bullet in the lands, then it will work fine.

So, if you don't adjust the load, how much difference in pressure does it make? It depends on the bullet and throat geometry. RSI has a Pressure Trace instrument example of a 6mm bullet increasing pressure by 20% moving the last 0.030" into the lands. Dr. Lloyd Brownell's study of absolute pressure conducted at the University of Michigan in the mid 1960's has an example of a round nose bullet with its much more gradual taper only making around 10% difference at any distance off the lands and until seating depth became so great it started to raise pressure by taking up powder space. VLD's also have a fairly gradual effect on pressure because of their large ogive radii. This all happens because, according to Dr. Brownell, what causes the pressure rise is not friction, but the amount of gas that is no longer allowed to bypass the bullet before it jumps from the neck and seals the bore.

I suggest reading through Berger's Tech Talk piece on making VLD's shoot well. They have to move them in fairly larger increments to see a difference. A bullet with a faster taper will probably want smaller increments of adjustment. The 20% rise measured by RSI is about as much as I've seen. A fellow using the same pressure instrument on another board saw no detectable peak pressure difference from touching the lands with a VLD and backing it off 0.030". This also is affected by how much robbing the case of powder space raises pressure as the bullet seats deeper. That and the bypass gas cutoff are effects that work in the opposite direction as the bullet seats deeper, so it follows that with some long enough bullets in some cartridges they could completely neutralize one another.

I also suggest that if you are going to start with a bullet in the lands, the powder charge be reduced a full 10%. That will reduce pressure between 20% and 30%, depending on the powder and bullet and chamber. That will keep you safe. (You should be safe in any case, as all this pressure difference is still below proof load levels; there just isn't any pointing putting extra wear and tear on the gun.) Work the load up from there. If you have a chronograph and you know what velocities you are getting from normal loads at normal seating depths, you should be able to get to the same velocity with the same exact powder, primer and case combination when you are touching the lands before the pressure gets too high.

Metal god · January 30, 2016, 12:11 PM

UN

I've read seating closer to the lands raises pressure more/faster then seating the bullet deeper in the cases when measurements are equal . Meaning lets call it a neutral seating depth of 2.800 for 308 . If you seat the bullet .025 longer and touch the lands . The pressure will be higher then if you seated the bullet .025 deeper in the cases . Is that a generally accurate statement ? It was my understanding the bullet needs to be seated significantly deeper to raise pressure to a point of concern . Exceptions being cartridge/bullet combos that start out with the bullet seated quite deep . 223 Rem and 77gr smk @ 2.260 comes to mind .

noylj · January 30, 2016, 06:54 PM

First, determine the COL and then work-up the load.
Bottleneck cartridges, reportedly, have pressure effects opposite to handgun cartridges.
Supposedly, due to the size of the case compared to COL, seating the bullet deeper actually lowers pressure and seating longer can cause the bullet to pause as it enters the rifling and that can raise pressures. None of this matters if you work up the load at a specific COL.
When I can, I work-up the load with the bullet as close to the rifling as possible without jamming the bullet into the rifling or so the COL just fits the magazine.

January 28, 2016, 10:21 PM	#1
Mosin-Marauder Senior Member Join Date: April 18, 2014 Location: North Carolina Posts: 2,320	Is too much OAL dangerous? I was loading some 7.62x54R in my Mosin with 51.2 grains of H4350 and a 174 Grain SMK, and I was wondering, if I seated them too long could it harm my rifle or me? I seated them pretty long and when I tried to chamber them it chambered fine, and I got rifling marks from just below the Ogive down to about a 16th of an inch above the middle of the case. I think it may like shooting off of the lands, I've since seated them a bit shorter (maybe a sixteenth more into the case) would this be dangerous for my rifle or me? Just thinking about pressures and stuff I just thought I would be better to ask than to not. Thanks for your help!

January 29, 2016, 05:10 PM	#6
Unclenick Staff Join Date: March 4, 2005 Location: Ohio Posts: 21,131	Mosin-Marauder, Allow me to correct some of the above. Many bullets shoot best seated into the lands. Benchrest shooters did this routinely for years. When I went to Mid Tompkins Long Range Firing School, he explained that he and his whole family of world champion long range shooters use "soft seating", where in the neck tension is minimal and the bullet is seated out too far on purpose and finishes seating using the throat as the seating dies when they chamber the round. Berger recommended seating its VLD bullets 0.010" jammed into the lands for years. The reason people fear seating into the lands, other than the problem of pulling bullets that T'Ohier mentioned (and that is a problem Tompkins mentioned; you have to be at a range that allows you to point the muzzle up while unloading if you are going to use this method), is that it raises pressure if you don't adjust the powder charge to compensate. But if you develop the load from the start with the bullet in the lands, then it will work fine. So, if you don't adjust the load, how much difference in pressure does it make? It depends on the bullet and throat geometry. RSI has a Pressure Trace instrument example of a 6mm bullet increasing pressure by 20% moving the last 0.030" into the lands. Dr. Lloyd Brownell's study of absolute pressure conducted at the University of Michigan in the mid 1960's has an example of a round nose bullet with its much more gradual taper only making around 10% difference at any distance off the lands and until seating depth became so great it started to raise pressure by taking up powder space. VLD's also have a fairly gradual effect on pressure because of their large ogive radii. This all happens because, according to Dr. Brownell, what causes the pressure rise is not friction, but the amount of gas that is no longer allowed to bypass the bullet before it jumps from the neck and seals the bore. I suggest reading through Berger's Tech Talk piece on making VLD's shoot well. They have to move them in fairly larger increments to see a difference. A bullet with a faster taper will probably want smaller increments of adjustment. The 20% rise measured by RSI is about as much as I've seen. A fellow using the same pressure instrument on another board saw no detectable peak pressure difference from touching the lands with a VLD and backing it off 0.030". This also is affected by how much robbing the case of powder space raises pressure as the bullet seats deeper. That and the bypass gas cutoff are effects that work in the opposite direction as the bullet seats deeper, so it follows that with some long enough bullets in some cartridges they could completely neutralize one another. I also suggest that if you are going to start with a bullet in the lands, the powder charge be reduced a full 10%. That will reduce pressure between 20% and 30%, depending on the powder and bullet and chamber. That will keep you safe. (You should be safe in any case, as all this pressure difference is still below proof load levels; there just isn't any pointing putting extra wear and tear on the gun.) Work the load up from there. If you have a chronograph and you know what velocities you are getting from normal loads at normal seating depths, you should be able to get to the same velocity with the same exact powder, primer and case combination when you are touching the lands before the pressure gets too high. __________________ Gunsite Orange Hat Family Member CMP Certified GSM Master Instructor NRA Certified Rifle Instructor NRA Benefactor Member and Golden Eagle

January 30, 2016, 12:11 PM	#7
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,885	UN I've read seating closer to the lands raises pressure more/faster then seating the bullet deeper in the cases when measurements are equal . Meaning lets call it a neutral seating depth of 2.800 for 308 . If you seat the bullet .025 longer and touch the lands . The pressure will be higher then if you seated the bullet .025 deeper in the cases . Is that a generally accurate statement ? It was my understanding the bullet needs to be seated significantly deeper to raise pressure to a point of concern . Exceptions being cartridge/bullet combos that start out with the bullet seated quite deep . 223 Rem and 77gr smk @ 2.260 comes to mind . __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again .

January 28, 2016, 10:45 PM	#2
reynolds357 Senior Member Join Date: December 10, 2012 Posts: 6,165	It would not be dangerous unless your load was already bordering on being overpressure. Eliminating the "jump" to the rifling raises pressure slightly.

January 28, 2016, 11:14 PM	#3
Tsquared Senior Member Join Date: January 26, 2016 Location: NE Atlanta Posts: 337	You don't want to have your bullets touching the lands of the rifling. Keeping the bullet off the lands as it has an affect on accuracy and an important affect on safety in regards to pressure. You need a little jump there.

January 28, 2016, 11:27 PM	#4
Mosin-Marauder Senior Member Join Date: April 18, 2014 Location: North Carolina Posts: 2,320	Roger that, I'll back down the bullet until it is barely off the lands.

January 29, 2016, 02:22 PM	#5
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	Bullet would get pushed into the case or gets stuck in the rifling and stops going into the chamber. What usually happens is the bullet gets pulled out and powder goes everywhere upon opening the action. Your rifling marks indicate your OAL is too long though. Max OAL with the bullet is 3.037". The off the lands stuff is a load tweaking technique that you can do after finding the load. Very much doubt it'll make any difference with a milsurp Mosin-Nagant.

January 30, 2016, 06:54 PM	#8
noylj Senior Member Join Date: October 21, 2007 Location: Between CA and NM Posts: 860	First, determine the COL and then work-up the load. Bottleneck cartridges, reportedly, have pressure effects opposite to handgun cartridges. Supposedly, due to the size of the case compared to COL, seating the bullet deeper actually lowers pressure and seating longer can cause the bullet to pause as it enters the rifling and that can raise pressures. None of this matters if you work up the load at a specific COL. When I can, I work-up the load with the bullet as close to the rifling as possible without jamming the bullet into the rifling or so the COL just fits the magazine.