Interesting obseravation

[rembolt]

Being a reloader it is fun to tinker with loads . here are some of the results of tinkering with a factory 6.5x55 se load . what I did was pull one bullet from one of the cartridges in the box of 20 . using my hornady oal gauge I calculated a oal of 20thou off the lands for that bullet . I then used a kenetic hammer to lengthen oal of the factory round in 5 of the cartridges . the bullet was then reseated to the corrected length of 20 thou off the lands using a seating die .
Commercially available 6.5x55 se 140gr soft point was the ammo used .the rifle is a Tikka T3 hunter in the above cal .

5 factory rounds fired over my chrony
1----2493fps
2----2453fps avg velocity 2460fps
3----2449fps vel spread of 45fps
4----2460fps
5----2448fps

5 modified for length cartridges using the same chrony
1----2487fps
2----2480fps avg velocity 2497fps
3----2503fps avg spread of 40 fps
4----2520fps
5----2495fps

Yes what you see is that the 5 cartridges with the corrected length avg a better velocity over all . I got to say I was surprised with the results as to my way of thinking avg velocity should have dropped .bumping the bullet ahead should have created more volume in the case thus lowering pressure . unfortunately I have miss placed the target these 10 rounds were fired at so I can not compare groups but I do recall the tinkered rounds shot a fair bit better group as well .

 

[WeakKnee]

Interesting, do you remember what brand of ammo you were shooting?

 

[rembolt]

Yes S&B 140gr soft point . I have that info in my load book with the data above just can't find the target to verifie the groups .

 

[Ganderite]

The closer you get to the rifling, the greater the pressure, with a significant increase when the bullet is engaged in the rifling. If the bullet is allowed to pop off the crimp and move with the pressure increase (seated deep) the pressure will be reduced.

If one day you find your self with ammo that is too hot for the rifle (popping primers) but you just HAVE to shoot (say a big match) there are 2 things you can do to reduce pressure.

If you have a seater die (don't need a press) put round on the table, put seater die on the round so die is on the table, and then screw down seater stem until it hits the bullet. Then give the stem a half turn (this will seat bullet about 25 thou deeper), then give the die a slap with your hand ( or a piece of wood). This will pop bullet a bit deeper and will reduce pressure.

The other way is to smear a film of grease on the ogive of the bullet. use the same grease you use to grease your locking lugs. This will reduce pressure about 5,000 psi.

 

[rembolt]

No visible difference in the primers from the 2 groups of cartridges . yes it is apparent that the rounds with less jump to the land are building more pressure and a more consistent velocity .

 

[curseyou]

The closer you get to the rifling, the greater the pressure, with a significant increase when the bullet is engaged in the rifling. If the bullet is allowed to pop off the crimp and move with the pressure increase (seated deep) the pressure will be reduced.

If one day you find your self with ammo that is too hot for the rifle (popping primers) but you just HAVE to shoot (say a big match) there are 2 things you can do to reduced pressure.

If you have a seater die (don't need a press) put round on the table, put seater die on the round so die is on the table, and then screw down seater stem until it hits the bullet. Then give the stem a half turn (this wills eat bullet about 25 thou deeper) than then give the die a slap with your hand ( or a piece of wood). This will pop bullet a bit deeper and will reduce pressure.

The other way is to smear a film of grease on the ogive of the bullet. use the same grease you use to grease your locking lugs. This will reduce pressure about 5,000 psi.

 

[Dogleg]

You're seeing about what I'd expect. Seating to the lands raises pressures. Increasing volume lowers pressure. Two factors, working in opposite directions. In this case the short jump won. In a straight wall rifle or pistol, increased case volume might win out. Sort of
like a Tug-o-war..

 

[bigedp51]

Sorry the devil made me do it.

 

[Alpheus]

I once did something similar in a 284 Shehane. Developed the load just off the lands, and then shot a few groups with increasing jump. Velocity slowly but steadily decreased. Of course, once you start reducing the internal volume too much, it will override the pressure-reducing effect of the jump and pressure will increase again.

 

[sail32]

.30-06 greased ammunition.

" The possible danger of the high power community's use of incorrectly greased bullets caused the authorities to withdraw, and scrap, the remaining ammunition out of concern for the safety of the shooter. This was not the first time that greased bullets were considered dangerous and withdrawn from service. In 1857 Seypoy troops of the Old Indian Army mutinied when given bullets that they believed were lubricated with animal fat, the use of which would have caused them to break dietary laws or lose caste. Seventy-five years later the jury is still out as the controversy simmers about just what part, if any, grease may have played in the National Match ammunition woes of 1921."

From;

A Short History of National Match Rifle Ammunition;

http://kysrpa.org/2010/history-of-national-match-rifle-ammunition

The Swiss also grease their GP-11.

The GP-11 was issued with a wax ring at the case mouth and some shooters had a device for greasing the bullet.

https://www.tapatalk.com/groups/theswissriflesdotcommessageboard/greasy-bullets-t1959.html