Money Line coversion from favorite to underdog HELP PLEASE

I tried to create a straight line conversion, but what the books are showing doesn't line up. 

If team B is a -300 favorite, shouldn't team A be at +280?  The books show the underdog to be at +250.  What is the proper conversion?

 I appreciate all help.

team A team B
-110 -110
-109 -111
-108 -112
-107 -113
-106 -114
-105 -115
-104 -116
-103 -117
-102 -118
-101 -119
100 -120
101 -121
102 -122
103 -123
104 -124
105 -125
106 -126
107 -127
108 -128
109 -129
110 -130
111 -131
112 -132
113 -133
114 -134
115 -135
116 -136
117 -137
118 -138
119 -139
120 -140
121 -141
122 -142
123 -143
124 -144
125 -145
126 -146
127 -147
128 -148
129 -149
130 -150
131 -151
132 -152
133 -153
134 -154
135 -155
136 -156
137 -157
138 -158
139 -159
140 -160
141 -161
142 -162
143 -163
144 -164
145 -165
146 -166
147 -167
148 -168
149 -169
150 -170
151 -171
152 -172
153 -173
154 -174
155 -175
156 -176
157 -177
158 -178
159 -179
160 -180
161 -181
162 -182
163 -183
164 -184
165 -185
166 -186
167 -187
168 -188
169 -189
170 -190
171 -191
172 -192
173 -193
174 -194
175 -195
176 -196
177 -197
178 -198
179 -199
180 -200
181 -201
182 -202
183 -203
184 -204
185 -205
186 -206
187 -207
188 -208
189 -209
190 -210
191 -211
192 -212
193 -213
194 -214
195 -215
196 -216
197 -217
198 -218
199 -219
200 -220
201 -221
202 -222
203 -223
204 -224
205 -225
206 -226
207 -227
208 -228
209 -229
210 -230
211 -231
212 -232
213 -233
214 -234
215 -235
216 -236
217 -237
218 -238
219 -239
220 -240
221 -241
222 -242
223 -243
224 -244
225 -245
226 -246
227 -247
228 -248
229 -249
230 -250
231 -251
232 -252
233 -253
234 -254
235 -255
236 -256
237 -257
238 -258
239 -259
240 -260
241 -261
242 -262
243 -263
244 -264
245 -265
246 -266
247 -267
248 -268
249 -269
250 -270
251 -271
252 -272
253 -273
254 -274
255 -275
256 -276
257 -277
258 -278
259 -279
260 -280
261 -281
262 -282
263 -283
264 -284
265 -285
266 -286
267 -287
268 -288
269 -289
270 -290
271 -291
272 -292
273 -293
274 -294
275 -295
276 -296
277 -297
278 -298
279 -299
280 -300

Doesn't work that way.

There isn't one for 2 reasons.

1) Different bets have different amounts of juice.  So it could be -110/-110 for a normal amount of juice, but -110/-120 for more juice ( on a prop bet)

2) There is a bigger difference in the ML on bigger favorites.  You will usually see -10000/+1400 or so for big favorites. Books usually won't get balanced action on this, so they want to give worse odds

They make it like that to keep you from being able to hedge on a huge favorite

Don't forget that different books will have different amounts of action for a particular side due to the region that the book is located. Simply take for example, a Cowboys game in Texas vrs the Atlanta Falcons. The books in Texas will obviously have different lines due to the local team (heavy action on the local fave) and the same can be said for Atlanta and it's region. Then think about THAT line to other bettors in a different area, say for example, California. There it may have action equal on both sides. Hence no "universal/standard" conversion rate from ml fave to ml dog.. 

 it's basic math.. but it works with reciprocals.

if both sides are -110... then betting on one side for $1 win = 110/(100+110) = .524.... so to bet on both sides and hedge yourself , would be 1.048.... so casino takes .048 of every dollar bet asuming the casino is hedged.. that's on -110.... basically 1.048 is the pertinent number. and for the equivalent juice, two sides reciprocals must add up to that figure

if we do -400......... then it costs you 0.8 for you to end up with a dollar at the end if you win........ so the other side of the bet must be (1.048 - .8) =.248...

so you need to bet 0.248 to make one dollar, including your original.

$1 divided by 0.248 = 4.03.. but we need to subtract 1 from it for our investment... so 3.03..... so +303....

-400 and +303 gives same adjusted-juice as both sides being -110

and i'll post some other numbers but not show the work

 it's basic math.. but it works with reciprocals.

if both sides are -110... then betting on one side for $1 win = 110/(100+110) = .524.... so to bet on both sides and hedge yourself , would be 1.048.... so casino takes .048 of every dollar bet asuming the casino is hedged.. that's on -110.... basically 1.048 is the pertinent number. and for the equivalent juice, two sides reciprocals must add up to that figure

if we do -400......... then it costs you 0.8 for you to end up with a dollar at the end if you win........ so the other side of the bet must be (1.048 - .8) =.248...

so you need to bet 0.248 to make one dollar, including your original.

$1 divided by 0.248 = 4.03.. but we need to subtract 1 from it for our investment... so 3.03..... so +303....

-400 and +303 gives same adjusted-juice as both sides being -110

and i'll post some other numbers but not show the work

here are some other ones (assuming equiv of -110 juice)

-200 = +162.5

-300 = +236

-2000 = +950

-10000 = +1640

you see the gap gets bigger and bigger........................... one way to see it is the difference between 0.001 and 0.002 is small, the difference between (1/x) in this case = 1000 and 2000.......... the difference is probabilities is linear, the difference in their reciprocal is curved and asymptotic at zero

cliff notes: if you work with reciprocals i.e. assumed winning percentage, then it makes sense.............. odds quoted as 10 to 1 vs. 1 to 10 are curves and asymptotic at zero

if there was zero juice, then -300 and +300 does make sense and leave everyone perfectly hedged.

once you start adding juice, there is a gap between them and the gap grows bigger and bigger as you get to -1000 (for example)