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10 May 2012
@ 01:48 am (GMT)

Trevor Wilkes

Hi guys,
New to the forum and long range shooting so any good advice would be greatly appreciated so just for now focusing on reloading for my 300 sendero ultramag.I have nosler custom brass,178gr and 208gr amax projectiles,AR2217 and AR2225 wont be loading rifle through the magazine Im curious to what would agood OAL be and some load data for the 208 amax none in hornady manual also best choice for primers.Also have redding s type dies so feel free to comment on the good and the bad so far only been reloading for 12 months 22-250 and 270.


13 May 2012
@ 05:42 pm (GMT)

Nathan Foster

Re: 300rum
Hi Trevor, no worries, what you are trying to achieve is a learning curve for most folks.

OK, if you try to seat long (single feeding) there is a chance that your RUM throat is so long that even by this, you still won't be near the lands. In this instance, seating long can be counter productive as it merely inhibits the case neck from acting a concentric guide.

OK, so here is what you need to do.

Determine the max COAL. Go to the knowledge base, at the bottom of the left hand menu you will find an article about determining COAL. Please read this before reading the rest of this post.

Once you have determined the max COAL, set your verniers to this length, then lay a .300 RUM case inside the vernier, then lay a projectile in the vernier beside the case and push the projectile forwards to meet the opposite face of the vernier (see photo of .308 Win) and observe.

In the example photo below, the bottom A-max bullet is set to the max COAL touching the lands. But, there is a problem in that if the bullet is seated to this length (or even a 1mm/40 thou jump), the projectile is not seated deeply enough in the case for it to be truly square with the bore. In other words, The deeper the bullet is seated, the more square (concentric) to the bore and the more that case neck can act as a guide. The top projectile shows the optimum seating depth (it appears as 70mm but is actually 71mm / optical illusion due to slight camera lens angle). You can see how I have aligned the projectiles boat tail / bullet body junction with the case neck / shoulder junction.

Your magazine length is 94mm (Sendero) so you can seat to 93mm for smooth feeding.

So, find your max COAL, see how this looks in the vernier and then look at decisions. Please post back your measurements and findings, I like to keep up with trends in factory rifle throat lengths etc, it will be very helpful for everyone.

13 May 2012
@ 06:06 pm (GMT)

Nathan Foster

Re: 300rum
As for powder, ADI2225 (Retumbo) will be fine with the 208 grain bullet.

Not much point working with the 178gr at this stage unless you run into stability problems with the 208. Also, there is no point considering seating the 178 past your mag length and single feeding, its too short a bullet for this. If using the 178 after testing the 208 grain bullet, switch to 2217 (H1000).

Start load for the 208gr will be 89gr (the ADI manual is all up the creek with its .300 RUM loads if you look at the 200 and 220gr data).

Work up test loads in half grain increments. Work up to 91 grains and observe primers and extraction, scuff marks on shells etc. If no pressure signs are found, carry on until max is found. You will then have the full picture of what the rifle is capable of, where max is, where the sweet spots are. Nosler brass is unfortunately very soft in comparison to Rem brass but it will do.

Do not confuse wide groups with high pressure. If groups widen as loads are increased, it may well be due to the increased recoil calling for better shooting technique, prompting the shooter to lift his game to a whole new level of discipline. Read pressure by reading the cases and primers. If you have trouble reading cases, then reload your brass and check primer pocket resistance when seating new primers. If the pockets are loose, the pressure is too high. This is why it can be handy to work up only two to three grains at a time in half grain increments, reload the 15 to 18 cases again and check primer pocket resistance.

Above, spent primer 1 is flattened from high pressure, seen at point A.

Spent primer two is in good condition

Spent primer 3 is also in good condition. However, there is cratering at the point where the firing pin contacted the primer. This cratering is often misread as high pressure when it is in fact simply excessive firing pin protrusion or an over sized firing pin hole in the bolt. In either case, primer 3 is quite fine, everything is safe.
13 May 2012
@ 07:17 pm (GMT)

Trevor Wilkes

Re: 300rum
Hi Nathen,
Thanks for the reply very helpful will get back to you when rifle arrives and do some reloading with it Cheers.


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