Savage 12FV .223, SMK 53 grain, and mashed into lands revisited

[RussellC]

Some threads ago, I was asking how various lengths of bullets didnt fit the 12FV chamber.

While the SMK at 69 grains worked fine at Sierras suggested 2.260, the SMK in 52 and 53 grains did not fit at the suggested 2.250.

When chambered, the smaller bullets different ogive shape, when chambered would be mashed down to 2.235 or so. By reducing length to 2.230 or so, they chambered fine.

Now the question. My "guess answer" is this is fine or someone likely would have mentioned this in the previous thread.

It occurred to me that once fired, this bullet would jump forward the the point where the ogive "mashed" into the lands....is this typical? In my inexperienced mind, I wonder if this would cause an unsafe high pressure event, or does the bullet just cramp through the area of the "obstruction" harmlessly?

Is this only high pressure if the round fires while mashed into the lands?

Russellc

 

[LoonWulf]

Bullets will always "mash" into the lands when fired...thats kinda how rifling works

This is just be guessing, but i believer the high pressure that comes from bullets being stuffed into the lands at ignition has to do with objects at rest wanting to stay at rest. When the bullets already in motion it has momentum to help start the engraving/swagging process of transferring into the rifling.

Again thats mostly a guess as ive never bothered to figfure out WHY you dont stuff bullets into the rifling. Unless of course your one of those guys that sets up a gun and load like that.

 

[RussellC]

I figured it just made its way through fine, but wondered.

In my original thread, the 2.250 spec OAL suggested by Sierra "mashed" down to about 2.235 or so....several commented that this could cause a high pressure situation, from the force
shortened OAL, combined with bullet going off in this in the lands condition.

I really dont know, but just wondered. I always figured from reading about amount of jump to the lands some try to calculate, that some jump is desirable.

Thanks, I figured it just made its way through.

Russellc

 

[243winxb]

Weatherby uses an extra long free bore to increase the bullet jump. This reduces pressure.
There is a small pressure spike when the bullet engages the rifling. Normal and not a problem.

When a bullet is jammed into the rifling, the pressure is higher, by as much as 10,000 PSI. (If you believe the internet?)

Bench rest shooters , with custom chambers, may load with a jam. With the bullet already into the rifling, the pressure spike is avoided, as the bullet already has contact with the rifling. The added pressure helps powder burn better & cleaner. The jam aligns the bullet in the center of the chamber. Better accuracy.

Factory chambers , long throats, free bore, bullet jump, can produce very good accuracy.

SAAMI Definition

LEADE (LEAD)
That section of the bore of a rifled gun barrel located immediately ahead of the chamber in which the rifling is conically removed to provide clearance for the seated bullet. Also called Throat or Ball Seat.
FREE BORE
A cylindrical length of bore in a firearm just forward of the chamber in which rifling is not present. Associated with bullet jump.

 

[RussellC]

Thanks, as usual I figured you guys would no the answer to this curiosity.

Russellc

 

[Axis II]

im a savage man and i will tell you that no book OAL has ever fit my rifles. I just use the OAL tool and make my own.

 

[Sunray]

"...various lengths of bullets didnt fit..." One assumes you mean cartridge OAL not the bullet.
2.260" is the SAAMI max OAL(from the point to the flat with no ogives involved) for .223. If a loaded round at that OAL fits, but shorter loaded cartridge doesn't fit, it's not the OAL that's wrong. And the bullet is not being "mashed' anywhere. Most likely the case was not sized correctly, but that's just a WHAG.
"...cause an unsafe high pressure event..." Nope. The pressures are still growing at that point, but like water, the bullet goes down the path of least resistance. And that's the barrel.

 

[RussellC]

im a savage man and i will tell you that no book OAL has ever fit my rifles. I just use the OAL tool and make my own.

For my gun, the Sierra book spec for their 69 grain Match King, 2.260 works perfect... the Sierra 52 and 53 grain Match King, and the Sierra 53 grain HP do not.

Russellc

 

[Axis II]

For my gun, the Sierra book spec for their 69 grain Match King, 2.260 works perfect... the Sierra 52 and 53 grain Match King, and the Sierra 53 grain HP do not.

Russellc

v max, fmj, etc wont do book specs but sp will. just have to load for the gun at that point and forget book spec. when I sent mine to savage I inquired about the short throat and was told don't worry about it, it was for accuracy.

 

[LoonWulf]

Honestly Ive never had a short throated factory rifle, all of mine have been so long that with the really pointy bullets I would exceed mag length on almost all of them. Its kinda interesting that savage is using a shorter throat on the .223. I figured with my previous experience with their guns, and the hooplah about shooting 556 in .223 chambers they would run them long....kinda refreshing too, hate running out of mag space.

The short mag boxes are one of the reasons I prefer the remington 700 to the savage long actions when chambered in magnums, especially the .300 win.

 

[RussellC]

As an experiment, I made a dummy bullet that I believe was 2.280 with the 69 grain match king. It chambered no problem, and held its OAL. Oddly, the smaller match king and non match king (52 & 53 grain) with its funky shaped ogive wouldn't go beyond 2.235.

Russellc

 

[RussellC]

"...various lengths of bullets didnt fit..." One assumes you mean cartridge OAL not the bullet.
2.260" is the SAAMI max OAL(from the point to the flat with no ogives involved) for .223. If a loaded round at that OAL fits, but shorter loaded cartridge doesn't fit, it's not the OAL that's wrong. And the bullet is not being "mashed' anywhere. Most likely the case was not sized correctly, but that's just a WHAG.
"...cause an unsafe high pressure event..." Nope. The pressures are still growing at that point, but like water, the bullet goes down the path of least resistance. And that's the barrel.

No, I meant exactly what I said. Brass is sized fine. The OAL, like I stated was exactly what Sierra called for. One of the 3 tried fit, the other two did not. Oddly the longest heaviest bullet gave no problem, but like I said, due to the shape of the bullet, the two smaller ones would not work at Sierras recommended OAL

Instead, they crushed against the lands and shortened the over all length from 2.250 to 2.235. a couple of times, upon extraction, the bullet stayed in the gun. Nothing more, nothing less.

The 69 grain SMK could be loaded way beyond max magazine length... The 52 and 53 grain ones, much less than magazine max.

Russellc