17 MACH IV reloads

[Tallguy52]

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??

 

[450BM]

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…

 

[L.Sherm]

I've been around one that shot AA2230 extremely well

 

[L.Sherm]

Have you looked at your neck clearance i.e. loaded round vrs fired case neck dia.?

 

[JohnW...ski]

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.

 

[L.Sherm]

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.

 

[SeabeeKen]

Excellent point. When i made 223 into 20 vartarg, i had to turn the necks. Over .016” thick

 

[snert]

About the third range session when you hit that bolt handle you will have a two piece bolt and handle

 

[Tallguy52]

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.

 

[358WCF]

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.