• This Forum is for adults 18 years of age or over. By continuing to use this Forum you are confirming that you are 18 or older. No content shall be viewed by any person under 18 in California.

17 MACH IV reloads

I have been struggling to get the performance I want from 17 MACH IV reloads. Custom rifle, Rem 788 action, cases formed from RP 223 brass. Using magnum SR primers to prevent blown primers. Good accuracy with N133 powder.
15 grains N133 3,300 fps; bolt rotates and cycles-ejects case. 16 grains N133 3500 fps; bolt rotates requires light tap with plastic hammer to cycle-eject case. 17 grains N133 3700 fps; bolt rotates requires slightly harder tap with plastic hammer to cycle-eject case.
Primers aren't flattened. I had a gunsmith inspect chamber for roughness that might create extraction issues. He didn't see anything to cause concern.
I would like to achieve speed around 3,700 fps without case ejection issues.
Anyone have any ideas??
 
18.6 gr of IMR 8208, CCI 400 primer with a 20gr bullet gives me 3650 fps and very good accuracy. Action opens with ease.

Oh, I should add that this is a 17 Fireball with factory brass in a Rem 700…
 
My go to load is 25 gr. Hornady HP with 18.1 of N133 and Remington 7-1/2 primers. I am using resized Lapua .221 cases so I would think I have a little more case volume than a .223.

L.Sherm mentions neck clearance, that is more than a valid point, I don't know how you could get a resized .223 to work without either reaming the inside of the neck or turning.
 
I've seen MachIV reamer prints from .199- .205 neck chamber dia.
O.P. if your necks haven't been turned i would be doing some serious investigation on Neck chamber dia starting from your smith with a print.
Even if they have I would still figure out what your chamber nk dia is.
Look at what the .200 line is also and compare to a sized case, if the 223 brass has been once fired it could be to tight at the base now.
Most new 223 brass is .3735 or there abouts. Most reamers were set up for the smaller Fireball brass at the base.
 
Last edited:
Good points. Cases were turned and reamed to remove bulge in case neck ID. Loaded ammo measures .195-.196 with good digital calipers. Fired case necks .200.
Once-twice fired brass produces same results. I sized brass with a 223 smallbase die, didn't help.
I tend to think there is something with the action or chamber. I have used other powders with same results of slightly stuck cases.
Loaded ammo chambers easily.
 
I have been struggling to get the performance I want from 17 MACH IV reloads. Custom rifle, Rem 788 action, cases formed from RP 223 brass. Using magnum SR primers to prevent blown primers. Good accuracy with N133 powder.
15 grains N133 3,300 fps; bolt rotates and cycles-ejects case. 16 grains N133 3500 fps; bolt rotates requires light tap with plastic hammer to cycle-eject case. 17 grains N133 3700 fps; bolt rotates requires slightly harder tap with plastic hammer to cycle-eject case.
Primers aren't flattened. I had a gunsmith inspect chamber for roughness that might create extraction issues. He didn't see anything to cause concern.
I would like to achieve speed around 3,700 fps without case ejection issues.
Anyone have any ideas??

No experience with sub 22 cal here, but by the name of the cartridge I would hope for at least near 4000fps.

OP is chasing velocity but no mention of barrel length?

Isn't the 788 the weak sister of the Remington line with the locking lugs on the back of the bolt? It apparently didn't work out too well for Schultz & Larsen with their 7x61 Sharpe & Hart rifles either.
 

Upgrades & Donations

This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.


Click Upgrade Membership Button ABOVE to get Gold or Silver Status.

You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.


To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.

Forum statistics

Threads
165,800
Messages
2,203,285
Members
79,110
Latest member
miles813
Back
Top