300HAMR BARREL TWIST

[bobcat93]

Question about twist calculations.
Ive made a decision im going with a 300 hamr barrel. Ive gone up and down side to side with crazy ideas and thoughts on what i want to do .
And it keeps coming back to utilizing what i already have for economic reasons.
I have everything for any variations of the 223 covered with my bushing dies and trim mate
I want to shoot the 125gr seirra bullets
#2121 & # 2120
3000fps from a 20" barrel
From what i find it requires a 1-11 or 12 barrel twist.
For accuracy
( can this be done), can those bullets hit 3200 out of that case and barrel combo?

The data ahows 1-15 twist for the 300hamr using those bullets but i believe that data is for suppression

I want to order a barrel what barrel twist do i order?
And what velocities can i expect with out blowing primer pockets
I know some of you have a way of calculating these numbers much better then myself..
Thanks for any feedback.
I dont want to order a 1-15 twist if the math is say 1-11 or 1-12 twist do i
What do the targets say.
And why would the twist change from a bolt to a gas gun with no suppression involved in the calculations. Or maybe it only changes with a can on a barrel..i dont know because i do not have a need for one..my ears are wasted already..id rather buy more primers hahaha
Thanks

 

[Walt Krafft]

What is the intended purpose of the rifle? I would lean faster twist rather than slower.

 

[Oso]

Based on Bill Wilson’s extensive testing of twist rates while developing the 300HAM’R, he determined two twist rates that are optimal for the bullet weight range used in 300HAM’R.
90gr-130gr 1:15 twist
135gr-160gr 1:13 twist (no issue shoot the lighter bullets)

Note:
Suppressed or Non-suppressed has no bearing on twist rate.
Rifle Type (Bolt or AR15) has no bearing on twist rate.
Bullet (shape, design, weight & material) effect selection of twist rate.
Barrel Length can influence twist rate.

In order to fit within 2.26” magazine length (AR15) the bullets that work in 300HAM’R are typically flat based (short & stubby). These bullets are short with lots of bearing surface, and not elongated high BC boattail projectiles. As such this cartridges doesn’t require a fast twist rate (1:10) to stabilize the projectiles.

Out of my AR15 (16” / 1:15 twist) I am pushing 125gr Speers TNT at 2,450-2,500fps. I would expect that with 20” bolt rifle you might get you +2,600fps.

Wilson Combat - 300HAM’R Load Data

Some of the bullets that were designed for 300BO are too long to fit the 300HAM’R. This includes the 110gr Barnes TAC-TX as well as the 125gr SMK. The Sierra 125gr Pro Hunter is a good substitute for accurate projectile in 300HAM’R.

Bolt rifles don’t have the 2.26” magazine length restriction so bullet can be loaded longer. Most likely the 125gr SMK will fit the magazine, but question become it’s fit in chamber.
< I’ll load one up and see how bullet’s ogee fits the chamber gage.

 

[dellet]

Based on Bill Wilson’s extensive testing of twist rates while developing the 300HAM’R, he determined two twist rates that are optimal for the bullet weight range used in 300HAM’R.
90gr-130gr 1:15 twist
135gr-160gr 1:13 twist (no issue shoot the lighter bullets)

Note:
Suppressed or Non-suppressed has no bearing on twist rate.
Rifle Type (Bolt or AR15) has no bearing on twist rate.
Bullet (shape, design, weight & material) effect selection of twist rate.
Barrel Length can influence twist rate.

In order to fit within 2.26” magazine length (AR15) the bullets that work in 300HAM’R are typically flat based (short & stubby). These bullets are short with lots of bearing surface, and not elongated high BC boattail projectiles. As such this cartridges doesn’t require a fast twist rate (1:10) to stabilize the projectiles.

Out of my AR15 (16” / 1:15 twist) I am pushing 125gr Speers TNT at 2,450-2,500fps. I would expect that with 20” bolt rifle you might get you 2,600fps. However, the 125gr SMK is too long to fit within 2.26” mag limit. In a short action bolt rifle you should have adequate mag length. The question is how it fits within the standard HAM’R chamber….

Wilson Combat - 300HAM’R Load Data

The 125 SMK will work, outside of the mag length restriction . you might need to trim the neck short, how much will depend on how the brass fits the chamber. Base to ogive on the 125 SMK is roughly .440”. The nose length will be below the neck opening at 2.260”.

If you can load with the ogive at 1.850” as the chamber drawing shows. It should fit the chamber, and an AI magazine will fix the COL problem in a bolt action.

Stability might be questionable in a 1/15, 1/14 is no problem.

You can’t trust most of the online stability calculators for flat base bullets unless you can input bullet dimensions. A drag calculator works better.

 

[Dufas]

IIRC, 1:13 is only one made anymore from Wilson.

 

[Oso]

I dropped a 125gr SMK into factory new Starline 300HAM’R case. Using the bullet seating gage mirror’s chamber) I seated the SMK until it just fit into gage (base of case is flush with bottom of gage). This measurement would be touching the lands.

 

[dellet]

I dropped a 125gr SMK into factory new Starline 300HAM’R case. Using the bullet seating gage mirror’s chamber) I seated the SMK until it just fit into gage (base of case is flush with bottom of gage). This measurement would be touching the lands.

View attachment 1737586

View attachment 1737588

https://mdttac.com/us/223-mdt-metal-aics-magazine

3000 fps is still a dream

 

[Oso]

IIRC, 1:13 is only one made anymore from Wilson.

Savage has announced that several versions of their Model 110 bolt rifles will be chambered in 300HAM’R.

Edit: rifles have 16.5” barrel (1:12 twist)

 

[Oso]

Dellet - 125gr TNT is stable in 1:15 barrel. What/why the concern around the 125gr SMK?

Both are flat based with plenty of bearing surface.

 

[bobcat93]

So go with what Willson came up with?
Order a 1-15 twist?
And that will cover the 100gr-150gr bullets

 

[dellet]

Dellet - 125gr TNT is stable in 1:15 barrel. What/why the concern around the 125gr SMK?

Both are flat based with plenty of bearing surface.

TNT .920”
SMK 1.150”
Part of stability is how easy it is to overturn a bullet. The SMK has a longer lever. The actual terms for what you’re looking at is Center of gravity, VS Center of pressure, the distance between is how easy the bullet will tumble, in the easiest terms.

Here’s a drag form calculator that’s pretty easy to use. Most want measurements in calibers. Bearing surface is 1.5 calibers long, instead of .454” long. That will give you a better idea.

Also remember that 1.6 sg and above is for maximum BC. Bullets won’t tumble until down around 1.2 sg even less depending on the bullet. I think Sierra told me 1/14 years ago.

Then back to the best example. Berger lists the minimum twists for their bullets. Run the flat base 308’s through their own provided calculator that they tell you won’t work for flatbase bullets and compare what you get vs what the recommend in the bullet spec section.

External Ballistics form

Ballistics Programs

www.geoffrey-kolbe.com

 

[Oso]

The 125 SMK will work, outside of the mag length restriction . you might need to trim the neck short, how much will depend on how the brass fits the chamber. Base to ogive on the 125 SMK is roughly .440”. The nose length will be below the neck opening at 2.260”.

If you can load with the ogive at 1.850” as the chamber drawing shows. It should fit the chamber, and an AI magazine will fix the COL problem in a bolt action.

Stability might be questionable in a 1/15, 1/14 is no problem.

You can’t trust most of the online stability calculators for flat base bullets unless you can input bullet dimensions. A drag calculator works better.

I should have included this photo with the others above. This is Cartridge Length (Case Base to Bullet Ogee) measured with Sinclair’s Bullet Seating Gage. The WC Bullet Seating Gage is cut to mirror the chambers in their barrels. It is a good starting point… but keep in mind your rifle’s chamber will vary.


Disclosure - my measurements are based on my tools, which may differ from yours.

 

[Oso]

TNT .920”
SMK 1.150”
Part of stability is how easy it is to overturn a bullet. The SMK has a longer lever. The actual terms for what you’re looking at is Center of gravity, VS Center of pressure, the distance between is how easy the bullet will tumble, in the easiest terms.

Thanks. I hadn’t tried loading the SMK in anything other than 300BO so hadn’t even given it any thought. Math & Facts always beat the Lazy Guess

 

[dellet]

Thanks. I hadn’t tried loading the SMK in anything other than 300BO so hadn’t even given it any thought. Math & Facts always beat the Lazy Guess

This why I keep saying that the biggest limiting factor for both cartridges is the magazine. The Hamr even more so. There are some 150 grain Hunting VLD bullets that you could easily get 24-2500 fps in a bolt action with a 20-22” barrel.

I think a Savage with 1/12 twist would be very interesting for a hand loader thinking outside the box. 1/10 and some 168-175 grain bullets would make some people stop and think.

 

[bobcat93]

Push that bullet in the case and lets see what 2.250" looks like

 

[bobcat93]

https://mdttac.com/us/223-mdt-metal-aics-magazine

3000 fps is still a dream

Yeah that sucks .ive used those flat base bullets on deer and have watch them take a step and flop over in the woods. Wish i could just cram them in my 30-30 magazine
I see savage is coming out with a new rifle as some one mentioned.
Its cool but ive already have a tuned up savage..all i need to do is change the barrel and pew pew im in buisness..
3000fps pipe dream
If i want to push a 308 125 3000 i need about 48gr. Case capacity..
The hamr is down about 26 hahaha
So be it the 300Hamr is a cool modern 30-30win.
I bet its fantastic in a bolt gun. Hell i could use a 300blackout..but i want a little more poof!
The black out would make sense also as i shoot mostly fireball based cartridges but its like shooting a 32-20 kind of uneventful for the intended purpose..
Hitting steel, deer, paper on a budget

 

[Oso]

I have loaded 2nd dummy round with goal of seating 125gr SMK to 2.25” COAL.



You will note that at 2.330” the bullet is seated too deep with the ogee now being inside case mouth/neck. This is a No Go so I stopped seating it any deeper. 125gr SMK will not fit inside 300HAM’R while staying within AR15 mag length restriction.

 

[Oso]

Here are a couple of intermediary seating depth.


Red polymer tip pointing at top of bearing surface where Ogee begins.


At approx. 2.359” COAL the bearing o bearing surface was seated completely in the case neck with the beginning of Ogee starting right in front of case mouth. This is as short as can seat this bullet inside 309HAM’R

The cases used for this exercise a new factory cases made by Starline. The average case length is approx. 1.596” from Starline, with the case neck being 0.230”. At 1.596” case length these are toward the shorter end of SAAMI spec.

 

[426nut]

Need 3k, might be time for a 30 BR?

 

[bobcat93]

Wow!..that was very deceiving..i dont have any equipment in front of me. So i have no way to answer my own questions with out asking..it sucks i feel naked.
The first photo looked like it had a lots of space to be pushed in to the case.

Thank you Oso..i appreciate your willingness to examine this subject for an inquiring mind.

I have never ever experienced such an anomaly in shooting and reloading. But then again ive never explored small 308 cartridges
I only have experience with the 300 magnums & the 30-30 when it comes to the world of 308 ..
Things work differently when you start taking away case capacity.
With a bullet diameter of .308
Not that its not the same with other cartridges.
But there is a turning point once you hit a certain diameter projectile.
It takes great energy to get a 308 caliber bullet moving.
Why is that?
Is there a name for it?
I suppose this relationship is shown when folks speak about shooting a
308win vs a 7mm-08 im told the 7mm-08 is very soft compared to the 308 win
But i cant speak from experience